Lithium Battery Calculator & Sizing Guide

Battery sizing is not simply an Ah calculation. A 20Ah battery may contain enough energy to run a device and still be unable to start it if the startup current exceeds the BMS or cell limits.

A useful lithium battery calculator therefore needs to answer two fundamental questions:

How much energy must the battery store?

Can the battery deliver the power the equipment requires?

The calculator provides a preliminary estimate. The sections below explain how to translate that result into a battery pack requirement that can be reviewed for manufacturability.

Important: Calculator results are preliminary sizing estimates. Final battery specifications depend on the confirmed cell, operating voltage window, current profile, BMS, temperature, mechanical design, charging system, and applicable compliance requirements.

What Battery Size Do You Actually Need?

"Battery size" is not defined by a single number.

Two batteries can both be rated at 20Ah but contain very different amounts of energy if their voltages differ. For battery pack design, capacity, energy, voltage, and physical dimensions can all matter at the same time.

That is why an effective sizing process starts with the equipment requirements rather than simply looking for a battery with a higher Ah rating.

The Four Key Inputs You Need Before Calculating Battery Capacity

Before entering a capacity value into an RFQ, collect four key parameters from the device.

Device Operating Voltage

Voltage is the first design constraint to establish.

Whenever possible, use the equipment's electrical specification rather than simply the voltage printed on the charger. Some devices specify a nominal system voltage, while others specify an allowable input-voltage range. A "24V-class" device does not mean the battery remains at exactly 24.0V throughout the discharge cycle.

The final pack design must eventually consider:

nominal battery voltage;

full-charge voltage;

discharge cutoff voltage;

device input range;

charger compatibility;

and the voltage limits used by the BMS.

For an OEM project, record the equipment's voltage requirement before calculating Ah.

Continuous Power or Current

You do not necessarily need both power and current.

If the equipment specification provides power:

P = V × I

and therefore:

I = P ÷ V

If the device is marked 24V / 5A, the basic load is approximately 120W.

If the device is marked 24V / 120W, the basic current is approximately 5A.

Use a load value that reflects the actual operating condition. The maximum nameplate value may be useful for checking current capability, but it can overestimate energy consumption if the equipment rarely operates continuously at that level.

When the load varies significantly over time, create a load profile rather than relying on a single value.

Required Runtime

A battery delivers energy over time, so power alone cannot determine the required capacity.

Define the operating requirement precisely:

eight hours continuously;

one eight-hour work shift with intermittent loading;

standby plus active operation;

a number of operating cycles;

or one full working day between charging events.

For example, equipment may be powered for eight hours while operating at a high load for only 40% of that time. In that case, assuming eight hours at full load may not reflect the actual energy requirement.

For variable industrial loads, divide the operating cycle into operating modes and calculate the energy consumed in each mode.

Peak or Startup Current

Energy requirements and current requirements are different.

Equipment containing motors, pumps, compressors, solenoids, actuators, robotic drives, or other dynamic loads can draw significantly more current during startup than during normal operation.

Collect at least the following:

continuous current;

peak current;

peak duration;

and, where relevant, repetition frequency.

A 25A pulse lasting 100 milliseconds is a different engineering condition from a 25A load lasting 10 seconds.

Peak demand can affect cell selection, BMS protection settings, wiring, connectors, voltage sag, and thermal behavior. It should be evaluated before the final BMS is selected.

Requirement Checklist

Before calculating, confirm:

System voltage

Continuous W or A

Required runtime

Peak W or A

Peak duration

How to Calculate Battery Capacity in Ah

When the Device Current Is Known

For a simple constant-current load:

Theoretical Capacity (Ah) = Current (A) × Runtime (h)

Example:

5A × 4h = 20Ah

This calculation indicates that the load theoretically consumes 20Ah over four hours.

It does not automatically mean a 20Ah nominal battery should be purchased.

The final nominal capacity may need to account for usable depth of discharge, system efficiency, operating temperature, aging requirements, load uncertainty, and engineering margin.

When Device Power Is Known

When the specification provides power in watts rather than current in amps, calculate energy first.

Step 1

Energy (Wh) = Power (W) × Runtime (h)

Step 2

Capacity (Ah) = Energy (Wh) ÷ Voltage (V)

Combined:

Ah = (W × h) ÷ V

This calculation still represents a theoretical value.

Worked Example

Assume an equipment requirement of:

Voltage: 24V

Continuous load: 240W

Runtime: 4 hours

First calculate energy:

240W × 4h = 960Wh

Then convert energy to capacity:

960Wh ÷ 24V = 40Ah

A 40Ah theoretical result is not automatically a 40Ah final pack recommendation. The next stage determines how much rated capacity the application actually needs.

Why the Theoretical Capacity Is Usually Too Small

A sizing calculation can be viewed at three useful levels:

Theoretical capacity → usable capacity → recommended preliminary capacity

The formula establishes the energy demanded by the load. Engineering assumptions determine how much nominal battery capacity is needed to deliver that energy under real operating conditions.

How Much Rated Capacity Can Your Design Actually Use?

Depth of discharge, or DoD, describes the portion of the rated capacity used before recharging.

The usable percentage should not be treated as a universal value for every lithium battery. It can depend on chemistry, cell manufacturer guidance, required cycle life, BMS limits, product strategy, and end-of-life requirements.

For illustration only, if a 40Ah battery is designed around 80% usable capacity:

40Ah × 80% = 32Ah usable

That example illustrates the relationship; it does not mean that every Greatech battery or every lithium chemistry should be designed around 80% DoD.

Why Doesn't All Rated Battery Energy Reach the Load?

Real systems have losses.

Depending on the architecture, losses can occur through:

internal cell resistance;

wiring;

connectors;

protection components;

DC/DC converters;

inverters;

and other power electronics.

Any efficiency assumption should therefore be stated explicitly and tied to the actual system architecture.

If an AC appliance is supplied through an inverter, for example, the battery must provide more energy than the AC load alone consumes because conversion is not lossless.

Temperature Derating

A battery that meets the runtime requirement at room temperature may not provide the same usable performance under the project's worst operating condition.

Cold conditions can reduce available discharge performance, while elevated temperatures can affect service life, thermal behavior, and allowable operating limits.

For a real OEM design, use the selected cell manufacturer's discharge curves and temperature limits rather than applying a universal "cold-weather percentage."

The design question is:

Will the battery still meet the required runtime and current at the actual minimum and maximum operating temperatures?

Battery Aging

Beginning-of-life capacity is not always the appropriate design target.

If the equipment must still achieve a specified minimum runtime after a defined service period, the project should consider expected capacity fade.

Relevant requirements may include:

expected cycle count;

calendar life;

operating temperature;

charge/discharge strategy;

and minimum end-of-life capacity.

The goal is not simply to oversize the battery, but to define whether the runtime requirement must be met only when the battery is new or throughout a specified portion of the product lifecycle.

Engineering Safety Margin

A useful preliminary model can be written as:

Recommended Energy or Capacity ≈ Theoretical Requirement ÷ Usable DoD ÷ Efficiency × Design Margin

The design margin should reflect project-specific uncertainty rather than a universal rule.

Possible reasons for adding margin include:

load variation;

manufacturing tolerance;

aging;

temperature;

accessory loads;

uncertain duty cycle;

future software or hardware changes.

Too little margin creates runtime risk, while too much margin increases pack volume, weight, cost, charging time, and potentially the certification scope.

Calculate Battery Runtime from Ah or Wh

The same equations can be applied in reverse when you already have a battery and want to estimate runtime.

Runtime Using Ah

For a basic constant-current load:

Runtime (h) = Battery Capacity (Ah) ÷ Load Current (A)

For example, a theoretical 20Ah battery supplying a constant 5A load gives:

20Ah ÷ 5A = 4 hours

Actual runtime should then be adjusted for the same usable-capacity, efficiency, temperature, aging, and current-rate considerations discussed above.

Runtime Using Wh

When battery energy and device power are known, use:

Runtime (h) = Battery Energy (Wh) ÷ Load Power (W)

If the calculation should reflect usable energy only, use usable Wh rather than nominal Wh.

DC Load vs AC Load

A DC system may have a relatively direct energy path:

Battery → DC electronics → Load

An AC system normally adds another stage:

Battery → Inverter → AC load

The inverter consumes energy and introduces conversion losses, so calculating runtime for an AC appliance directly from its rated power without accounting for the inverter can overestimate runtime.

Why Actual Runtime Differs From the Calculator

A calculator produces an estimate; validation requires the actual load profile and the selected battery architecture.

Ah vs Wh: Which Number Should You Use?

Ah Measures Charge Capacity

Amp-hours describe electrical charge capacity.

Ah is useful when comparing batteries within the same voltage class or calculating runtime against a known current draw.

Its limitation is that Ah alone does not tell you total stored energy when voltage changes.

Wh Measures Energy

Watt-hours describe stored energy:

Wh = V × Ah

For comparing batteries across different voltage classes, Wh provides a more meaningful basis for energy comparison.

Why Ah Alone Cannot Compare Batteries at Different Voltages

Consider two nominal examples:

12V × 100Ah ≈ 1.2kWh

48V × 100Ah ≈ 4.8kWh

Both batteries are labeled 100Ah, but the second stores approximately four times the nominal energy because the voltage is four times higher.

Therefore:

Same Ah does not mean same stored energy.

Ah and Wh are not competing measurements. They answer different engineering questions.

Capacity Is Not Enough: Check Continuous and Peak Current

This is one of the most important checks in OEM battery sizing.

Energy determines how long the battery may operate, while current capability determines whether it can deliver the required power.

Current capability determines whether the battery can power the equipment at all.

Continuous Discharge Current

A basic current estimate can be calculated from power:

I = P ÷ V

For a simplified 24V, 240W load:

240W ÷ 24V ≈ 10A

That 10A is not simply another number in the calculator. It influences:

cell current capability;

number of parallel cells;

BMS current rating;

wiring;

connectors;

protection components;

thermal behavior.

If system voltage changes significantly during discharge, or a DC/DC converter is involved, final current should be validated across the actual operating voltage range.

Peak Current

Peak current is not meaningful without a defined time duration.

A specification should ideally include:

peak magnitude;

duration;

repetition frequency;

operating voltage during the event.

A 25A pulse for 100 ms and a 25A load for 10 seconds can impose very different requirements on the cell and protection system.

Where possible, use the equipment datasheet or a measured current profile rather than estimating motor startup demand from average power alone.

Why a Battery Can Have Enough Ah but Still Fail

Consider this simplified case:

Calculated capacity requirement: 20Ah

Normal load: 8A

Startup load: 25A

BMS continuous rating: 10A

BMS peak capability: below the startup requirement

The battery may be fully charged and contain enough energy to meet the expected runtime.

However, when the equipment starts, the current spike may trigger BMS overcurrent protection and disconnect the pack.

This is not a capacity shortage.

It is a current-delivery mismatch.

Have a motor, pump, actuator, compressor, robotic drive, or other high-current load? Send the continuous and peak-current profile with your preliminary sizing result for review.

From Ah and Voltage to a Real Battery Pack

Once voltage, energy, capacity, and current are defined, the project can begin moving from a calculation to a physical battery architecture.

Select the Battery Chemistry

There is no single battery chemistry that is "best" for every project.

The selection should balance:

This table provides general design guidance; it is not a final specification.

Chemistry selection should ultimately be based on the specific cell model and the project requirements for energy, current, service life, temperature, safety strategy, cost, and packaging.

Determine Series Cells

A conceptual starting point is:

Series Count ≈ Target Nominal Pack Voltage ÷ Cell Nominal Voltage

However, pack design does not end with a simple division.

The final series count must also satisfy:

full-charge voltage;

discharge cutoff;

equipment input range;

charger compatibility;

BMS architecture.

The target should be a compatible voltage window, not only a nominal label.

Determine Parallel Cells

A preliminary capacity estimate is:

Parallel Count ≈ Required Pack Ah ÷ Cell Ah

The parallel count also affects current capability.

If one candidate cell cannot continuously supply the required pack current, additional parallel paths-or a different cell-may be necessary even when the Ah calculation appears sufficient.

Estimate the S/P Configuration

Series and parallel counts combine into configurations such as:

6S4P, 7S3P, or another architecture determined by the selected cell and target specification.

The preliminary configuration must consider:

cell nominal voltage;

cell capacity;

continuous current;

pulse-current capability;

thermal behavior;

mechanical envelope;

BMS architecture;

charger compatibility.

An S/P estimate is a design input, not an assembly instruction.

How BMS Requirements Affect the Battery Specification

A BMS should not be selected based on Ah alone.

Its requirements can change a battery design that otherwise appears correct in terms of voltage and capacity.

Continuous Discharge Rating

The BMS continuous-current capability must align with the actual equipment load under the expected thermal conditions.

A pack sized for a 10A continuous device cannot be considered complete simply because its cells contain sufficient Ah. Protection devices, MOSFETs, conductors, connectors, and thermal limits must all support the operating requirement.

Peak Current Rating

A rating such as "30A peak" is incomplete without knowing:

how long 30A is allowed;

how often the event can occur;

protection-delay behavior;

temperature conditions;

and whether voltage sag remains acceptable.

Always compare the equipment's current-versus-time profile with the selected BMS and cell data.

Charge Current

Discharge is only half of the battery specification.

Charging requirements may depend on:

desired charge time;

selected cell charge limits;

charger output;

BMS charge-current rating;

operating temperature;

system docking or power interface.

A request for "fast charging" can therefore affect the cell, BMS, connector, thermal, and charger design.

Protection Functions

Relevant functions may include:

The final protection strategy should be confirmed for the actual pack and application.

Communication Requirements

For a smart OEM battery, the BMS may also need to communicate with the host system through:

CAN;

SMBus;

UART;

or another project-specific interface.

Potential data includes:

SOC;

SOH;

voltage;

current;

temperature;

fault state;

operating status.

Once host communication is required, the BMS is no longer simply a current-protection component; it becomes part of the equipment's overall system architecture.

When Physical Space Limits Battery Capacity

A battery can be electrically valid yet mechanically impossible to integrate.

Available Enclosure Dimensions

For a custom project, provide more than rough battery-compartment dimensions.

Useful mechanical inputs include:

maximum L × W × H;

irregular shape restrictions;

insertion direction;

mounting points;

connector exit direction;

cable routing;

service clearance;

surrounding heat sources.

These details can determine whether a particular cell format or pack architecture is feasible.

Cell Dimensions

Stored energy cannot be compressed indefinitely; cell format and packaging place physical limits on the design.

Different cell formats change:

packing efficiency;

volumetric energy density;

thermal paths;

mechanical support;

assembly strategy.

The highest-capacity cell is not automatically the best packaging choice if it creates current, thermal, service, or structural constraints.

Wiring, BMS and Insulation Occupy Space Too

The internal enclosure volume is not equal to usable cell volume.

A finished pack may also need space for:

BMS;

wire harnesses;

connectors;

holders or spacers;

insulation;

structural support;

protective materials;

thermal spacing;

and design allowance appropriate to the selected cell format.

Do not determine the maximum number of cells from enclosure volume alone.

Energy Density Trade-Offs

Assume a product team says:

"We need eight hours of operation, but the available battery volume is only 180 × 90 × 60 mm."

The first engineering question should not be "Which battery has the highest Ah rating?"

Instead, clarify:

What is the exact voltage range?

What is the real load profile?

Is eight hours required at continuous maximum load?

What peak current is required?

What temperature range applies?

What lifecycle target is expected?

Is the enclosure absolutely fixed?

What weight limit applies?

If the required energy does not fit within the available volume, the project may need to reconsider the chemistry, cell format, equipment consumption, enclosure dimensions, runtime target, or another system constraint.

Battery Sizing Example for a Real-World Device

Consider an industrial mobile inspection unit.

Device Requirements

For illustration:

System class: 24V

Continuous load: 180W

Startup load: 400W

Required runtime: 8 hours

Maximum battery dimensions: project-defined

Operating temperature: project-defined

Cycle-life requirement: project-defined

The values below demonstrate the calculation method. They are not confirmed Greatech battery specifications.

Step 1 - Calculate Theoretical Energy

Assuming 180W continuous operation for eight hours:

180W × 8h = 1,440Wh

This is the theoretical energy demand.

If the equipment cycles between standby and active modes, replace the continuous-load assumption with a weighted operating profile.

Step 2 - Adjust for Usable Capacity

For illustration only, assume:

usable DoD: 90%;

overall system efficiency: 92%;

design multiplier: 1.15.

These assumptions are examples, not universal recommendations.

Estimated preliminary energy:

1,440Wh ÷ 0.90 ÷ 0.92 × 1.15 ≈ 2,000Wh

This demonstrates why the final nominal energy target may be significantly higher than the load's theoretical 1,440Wh requirement.

The actual values should be determined from the selected cell, lifecycle target, system architecture, environment, and project uncertainty.

Step 3 - Convert Energy to Ah

Using a simplified 24V calculation basis:

2,000Wh ÷ 24V ≈ 83Ah

Compare:

Theoretical capacity: 1,440Wh ÷ 24V = 60Ah

Illustrative preliminary capacity: approximately 83Ah

The gap comes from the stated design assumptions-not from a different capacity formula.

The final pack voltage may not be exactly 24.0V, so the final Ah requirement should be recalculated based on the selected battery architecture.

Step 4 - Check Continuous Current

Basic load current:

180W ÷ 24V = 7.5A

The pack therefore needs to support at least the actual continuous operating current across its valid voltage range.

Final cell, BMS, connector, and wiring requirements should include appropriate engineering allowance rather than being designed at exactly 7.5A with no consideration of transient load or conversion losses.

Step 5 - Check Peak Current

Simplified startup current:

400W ÷ 24V ≈ 16.7A

That figure is only an initial estimate.

The design must still confirm:

actual startup voltage;

actual measured peak current;

duration;

repetition;

cell pulse capability;

BMS protection behavior;

acceptable voltage sag.

Step 6 - Select Chemistry

Suppose enclosure volume is extremely tight. Energy density may receive higher weighting.

Suppose long service life and a different safety/lifecycle strategy dominate the project. Another chemistry may become more appropriate.

The correct conclusion is therefore not:

"The calculation says X, so always choose chemistry Y."

Instead:

Define which project constraint is most difficult to satisfy, then compare candidate cells against that constraint.

Step 7 - Define a Preliminary Battery Specification

A sourcing-ready requirement for the example might look like this:

This provides a much more useful starting point for an OEM battery manufacturer than the statement:

"I need a 24V lithium battery."

Send This Preliminary Specification for Engineering Review

Common Battery Sizing Mistakes

Calculator Results vs. Final Custom Battery Specifications

A calculator is valuable because it translates equipment requirements into measurable battery requirements.

However, requirement estimation and battery engineering are different stages.

A calculator answers:

"Approximately what must the battery deliver?"

Engineering answers the question:

"How can that requirement be implemented in a manufacturable, testable battery pack?"

A practical OEM development flow is:

Device Requirements → Calculator → Preliminary Specification → Engineering Validation → Prototype → Testing → Final Specification → Production

The final design must satisfy electrical, mechanical, thermal, safety, integration, manufacturing, and regulatory requirements simultaneously.

When Should You Ask a Battery Manufacturer to Review Your Design?

A simple calculator is usually enough when the objective is only a rough runtime or energy estimate.

A manufacturer or battery-engineering review becomes more valuable when multiple constraints interact.

Electrical Complexity

Review is recommended when the project includes:

nonstandard voltage;

high continuous current;

significant startup or pulse current;

fast charging;

complex power conversion.

Mechanical or Environmental Complexity

Engineering review becomes especially important when the project involves:

tight enclosure dimensions;

unusual pack shape;

weight limits;

waterproofing requirements;

low- or high-temperature operation;

vibration or other environmental constraints.

System Integration

A custom pack may require additional review if the battery must integrate with:

CAN;

SMBus;

UART;

a host controller;

a custom charger;

docking equipment;

SOC/SOH reporting;

system fault logic.

Compliance Requirements

Projects intended for medical, industrial, transportation, or regulated markets may require specific testing, transportation documentation, market certification, or customer qualification procedures.

The more these constraints interact, the less reliable a calculator-only selection becomes.

Information to Provide for Engineering Review

To help Greatech evaluate a custom battery project, prepare the following:

Device voltage / input range

Continuous load in W or A

Peak load in W or A

Peak duration

Required runtime

Maximum battery dimensions

Operating temperature

Charging requirement

BMS communication requirement

Target market / compliance requirement

Prototype quantity

Expected annual quantity

10. Technical Specifications

Preliminary Calculator & Battery-Project Specification Table

11. Applications

Industrial Mobile Equipment

Mobile industrial equipment often needs a combination of all-day runtime, repeated charging, moderate-to-high power, and a battery that fits a limited enclosure. The calculator helps equipment manufacturers define preliminary Wh, Ah, continuous current, and peak demand before entering a custom battery discussion.

Typical buyer: Industrial equipment manufacturer, OEM engineer.

Inspection and Measurement Equipment

Portable inspection devices may operate through mixed standby and active cycles rather than one constant load. Separating these operating modes can produce a more representative energy requirement while peak-current checks protect against underestimating sensors, pumps, illumination, actuators, or computing loads.

Typical buyer: Instrument manufacturer, technical sourcing team.

Robotics and Automated Equipment

Robotic platforms can combine processors, communication systems, motor drives, actuators, and transient loads. A battery selected from Ah alone may therefore be unsuitable even when calculated energy appears adequate.

Typical buyer: Robotics OEM, automation integrator.

Medical Carts and Mobile Medical Equipment

Mobile medical systems may have specific runtime, charging, integration, lifecycle, documentation, and compliance requirements. A preliminary calculation is useful for defining energy demand, but the final battery must be reviewed against the actual equipment and applicable requirements.

Typical buyer: Medical equipment developer or sourcing team.

Portable Professional Electronics

Field computers, communications equipment, test systems, monitoring products, and other portable electronics frequently require a balance between runtime, weight, size, and charging time.

Typical buyer: Product developer, contract manufacturer, distributor.

New OEM Product Development

During early product development, battery requirements often change as electronics, firmware, enclosure, and operating modes are refined. A structured sizing process allows engineering and procurement teams to update the energy requirement without prematurely committing the project to a specific battery model.

Typical buyer: OEM R&D team, purchasing engineer.
 

12. Product Comparison

13. How It Works: From Calculation to Custom Battery Supply

Step 1 - Define the Device Requirement

Provide operating voltage, continuous load, runtime, peak load, environment, and mechanical constraints. Better inputs produce a more useful preliminary specification.

Step 2 - Calculate Wh and Ah

Use power/current and runtime to establish theoretical energy and capacity. Keep the theoretical result separate from the later design target.

Step 3 - Apply Engineering Assumptions

Review usable capacity, efficiency, temperature, aging, and project-specific margin rather than applying universal percentages.

Step 4 - Check Continuous and Peak Current

Confirm whether the battery cells and BMS must support short startup pulses, repeated transient loads, or sustained high-current operation.

Step 5 - Submit the Preliminary Requirement

Send Greatech the calculator result together with the battery dimensions, charger information, communication requirements, operating environment, quantity, and target application.

Step 6 - Engineering Review and Prototype Definition

Candidate chemistry, cells, BMS, configuration, mechanical arrangement, connectors, and test requirements can be evaluated against the confirmed requirement.

Step 7 - Confirm Final Specification Before Production

Prototype performance, testing scope, compliance documentation, packaging, quantity, and commercial terms should be confirmed before moving into bulk production.

14. Quality Assurance

Quality Control Should Be Defined by the Final Battery Specification

Battery pack quality cannot be demonstrated by capacity alone. For an OEM project, inspection and test requirements should be tied to the agreed electrical, mechanical, protection, and system-integration specifications.

Depending on the final model and project, relevant verification may include cell matching, pack voltage, capacity, charge/discharge behavior, BMS protection functions, current performance, communication functions, connector configuration, insulation, dimensions, appearance, and other agreed acceptance criteria.

Greatech should provide confirmed quality-control and test information based on the final battery model rather than relying on generic claims that cannot be traced to a specific specification.

Documents to confirm for publication or buyer review may include:

Product datasheet

Battery specification

Inspection criteria

Test report

BMS protocol information

Compliance documentation

Packaging specification

Important: Certification and test-report availability must be verified for the specific model before being published as confirmed Greatech data.

15. Factory Strength & Supply Capability

Project-Based Battery Manufacturing Support From Greatech

Greatech is positioned as a manufacturer, supplier, exporter, and OEM/ODM battery pack partner for customers who need technical coordination before placing a custom or repeat order. Rather than quoting solely from a voltage-and-Ah request, the recommended workflow is to align the device load, runtime, peak current, dimensions, charging requirements, BMS, documentation, packaging, and quantity before confirming the production specification.

For purchasing teams, this creates a clearer basis for comparing quotations and reduces the risk of changing critical technical requirements after tooling, prototype preparation, or production planning has begun.

Supply Capability to Confirm Per Project

Factory-direct quotation based on specification and quantity

OEM/ODM battery pack support

Prototype or sample discussion

Bulk-order planning

Custom connector and harness requirements

Custom packaging requirements

Export-ready packaging options

Project-based technical communication

Lead-time discussion after specification confirmation

MOQ discussion according to model and project stage

Buyer Benefit: One requirement sheet can connect engineering, procurement, prototype evaluation, quality documentation, and commercial quotation.

16. Download Resources

Prepare Your Battery Project Before Requesting a Quote

Technical documents are most useful when they help buyers make informed decisions rather than simply filling a download page. The following resources are recommended for the Greatech website. Their actual availability should be confirmed before publishing download buttons.

17. Frequently Asked Questions

How do I calculate how many Ah of battery I need?

If the device current is known, theoretical Ah is current multiplied by runtime. For a 5A device running for four hours, the theoretical result is 20Ah. For a real battery pack, usable depth of discharge, efficiency, temperature, aging, current capability, and project margin may increase the required nominal capacity.

How do I calculate battery size from watts and runtime?

First calculate energy using Wh = W × hours. Then convert energy to Ah using Ah = Wh ÷ battery voltage. The result is a theoretical starting point. A final custom battery specification still needs current, voltage window, BMS, thermal, mechanical, charging, and cell-level validation.

How long will a 20Ah lithium battery last?

Runtime depends on the load current, battery voltage, usable capacity, efficiency, operating temperature, battery condition, and BMS cutoff behavior. For a simplified constant 5A load, 20Ah ÷ 5A gives four theoretical hours, but actual operating time may differ.

Is a higher-Ah battery always better?

No. Higher Ah can increase runtime within the same voltage class, but it can also increase battery size, weight, charging time, and cost. It may be unnecessary if the real project constraint is peak current, available space, communication, temperature, or another requirement.

How much extra battery capacity should I add as a safety margin?

There is no universal percentage suitable for every battery project. Margin should reflect known uncertainties such as load variation, temperature, aging, system efficiency, manufacturing tolerances, and lifecycle requirements. Oversizing without a reason can unnecessarily increase volume, weight and cost.

How does temperature affect lithium battery sizing?

The battery must meet its current and runtime requirements under the actual operating environment, not only at room temperature. Final temperature derating should be based on the selected cell data and battery design. Avoid assuming one fixed percentage for every lithium chemistry or product.

How do I calculate peak current for a battery?

For some loads, power divided by voltage provides an initial estimate, but motor and actuator startup behavior can be more complex. The equipment datasheet or a measured current-versus-time profile is preferable. Provide the peak magnitude, duration, and repetition frequency for battery and BMS review.

Can two batteries with the same Ah have different runtime?

Yes. If their voltages differ, they can store different amounts of energy. A 12V 100Ah battery and a 48V 100Ah battery do not contain the same Wh. Actual runtime also depends on the load, efficiency, usable capacity, temperature, and operating conditions.

When do I need a custom battery pack instead of a standard battery?

A custom pack becomes relevant when the project requires nonstandard voltage, tight dimensions, specific connectors, high or unusual current, BMS communication, special charging, environmental requirements, or integration that cannot be satisfied by a standard commercial battery.

What information should I send a battery manufacturer for a custom pack quote?

Send the device voltage or voltage range, continuous load, peak current and duration, target runtime, maximum dimensions, operating temperature, charging requirements, BMS communication needs, target market or certification requirements, prototype quantity, and expected production quantity.

Does Greatech support OEM/ODM battery projects?

Greatech supports OEM/ODM battery pack projects, including requirement review and project-based specification development. The exact customization scope, prototype policy, MOQ, tooling requirements, documentation, lead time, and production capability should be confirmed for each specific project before ordering.

Can I request battery samples, datasheets or test reports?

These should be discussed after the target specification or candidate model has been identified. Sample availability, datasheets, test reports, compliance documents, and associated lead times depend on the final battery configuration and should be confirmed with Greatech before being presented as model-specific commitments.