BATTERY CALCULATOR TOOLS
Sizing a new battery, checking how long yours will run, or replacing lead-acid? Choose the job below. Each calculator shows you which numbers to find.
Choose a calculator
Choose the question that matches your job. You can start with the numbers you have.
Starting with a new device? Use its power rating and the hours you need it to run.
Already have a LiFePO4 battery? Check roughly how long it can power your equipment.
Check the labels on your old batteries. That is enough to start sizing a LiFePO4 replacement.
AFTER YOU CALCULATE
Use the result to narrow down capacity. Then check startup power, the charger, wiring and available space. If any of those are unclear, send your figures to our engineers and we can review them with you.
Battery size depends on energy use, usable capacity and losses. Current limits and startup loads need a separate check.
Wh = V × Ah; 1 kWh = 1,000 Wh
Compare Wh, not Ah alone, when battery voltages differ.
Wh = Σ(W × hours × quantity × duty cycle)
A Wh input is already the total energy used during the selected period.
DC Wh ÷ DC efficiency + AC Wh ÷ inverter efficiency + standby Wh
DC devices and AC devices have different supply losses.
Required Wh = battery-side Wh × (1 + reserve) ÷ (DoD × temperature × health)
Less usable capacity means a larger battery is needed for the same load.
Runtime h = planned usable Wh ÷ average battery-side W
Temperature, ageing, duty cycle and conversion losses affect actual runtime.
A ≈ simultaneous battery-side W ÷ minimum working V
If the lowest operating voltage is unknown, the estimate uses 90% of nominal voltage.
Compare surge, inverter and BMS ratings at the same duration
A 5-second peak rating does not confirm that a longer surge is supported.
h = replace Wh ÷ (V × net charge A × efficiency) × completion factor
Nominal defaults: 95% charging efficiency and a 1.10 end-of-charge time factor.
Delivered Wh = nominal Wh × DoD × temperature × health × rate factor
Measured usable energy takes priority. There is no fixed Ah conversion ratio.
The questions we hear most often when sizing or replacing a battery.
Compare Wh when the voltages differ. Ah tells you capacity at a given voltage: a 25.6V 100Ah battery stores twice the nominal energy of a 12.8V 100Ah battery.
We need the battery voltage and the watts your equipment uses before we can estimate hours. Temperature, usable capacity and conversion losses will also affect the answer.
It can in some setups, but there is no fixed 2:1 rule. If you know the load and how long the old bank actually runs, use those figures. Otherwise, the replacement range must allow for ageing, discharge rate and how deeply the old bank is used.
Check it against the LiFePO4 battery you choose before reusing it. We need its charging profile, highest voltage and current, float or equalization settings, and the battery’s BMS limits. A matching voltage label is not enough.
Continuous current keeps the equipment running. Motors, pumps and compressors can draw much more when they start; the battery and BMS must support that peak for long enough.
Check the exact battery model. Its cells, BMS or heater may set different limits. Do not bypass low-temperature charging protection.
Series increases voltage while Ah stays the same; parallel increases total Ah. Before wiring batteries together, check that the model allows it and that the BMS, cables, fuses and battery condition are suitable.
Look for W on the nameplate or in the manual. You can also measure running power. For AC equipment, volts × amps gives VA rather than W unless you know the power factor; check motor startup power separately.
Some inputs, such as temperature, usable capacity and supply losses, may still be unknown. The result shows which values were assumed. Replace them with measured figures when you have them.
Engine starting, high-voltage vehicles, medical and life-safety equipment, fire protection, required backup and grid-connected storage need a project review. The calculator can help collect the load figures; an engineer still needs to check protection and compliance.
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