Battery Runtime Calculator
Calculate battery runtime step by step: Runtime (h) = Capacity (Ah) × Voltage (V) × DoD × Efficiency ÷ Load (W).
In short
Formula: Runtime (h) = Capacity (Ah) × Voltage (V) × DoD × Efficiency ÷ Load (W).
What this calculator does
Calculate battery runtime step by step: Runtime (h) = Capacity (Ah) × Voltage (V) × DoD × Efficiency ÷ Load (W). Worked example, questions and limitations included.
Use it to turn Battery capacity, Battery voltage, Load power, Usable depth of discharge, and the other shown inputs into a checked result you can compare, copy, or rerun with different assumptions.
The page shows the formula, a numeric worked example, and the assumptions that affect this electrical calculation.
Inputs and what they mean
- Battery capacity
- — number value.
- Battery voltage
- — number value.
- Load power
- — number value.
- Usable depth of discharge
- — Enter your battery's recommended limit, e.g. from the datasheet.
- Inverter / converter efficiency
- — Enter 100 for a direct DC load.
How to use it
- Enter each value in the unit shown next to the box (use the unit converter first if your numbers are in other units).
- Check the breakdown to see every intermediate step.
- Read the limitations before relying on the result.
Formula
Depth of discharge and efficiency are entered by you — no chemistry is assumed.
Percentages must be between 0 and 100.
Load is the average power; for a varying load, use an average over the period.
Runtime (h) = Capacity (Ah) × Voltage (V) × DoD × Efficiency ÷ Load (W).
Inputs used: Battery capacity, Battery voltage, Load power, Usable depth of discharge, Inverter / converter efficiency.
Worked example
12 V 100 Ah battery, 60 W load
- Stored: 100 × 12 = 1,200 Wh.
- Usable: 1,200 × 0.5 × 0.9 = 540 Wh.
- Runtime: 540 ÷ 60 = 9 hours.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
Limitations and assumptions
- No Peukert or temperature correction.
- Assumes a constant average load.
- Battery ageing reduces capacity over time.
- Results are estimates for planning and learning. Real designs, installations and bids must be checked by a qualified, licensed professional against the codes that apply where you work.
- The result depends on the values you enter for this battery runtime calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.
Common questions
Why is depth of discharge required?
Discharging some batteries fully shortens their life. Lead-acid is often limited to around half, while many lithium packs allow more. Use your datasheet figure.
Does high current reduce capacity?
Yes. Lead-acid capacity drops at high discharge rates (Peukert effect). This calculator does not model that, so fast discharges will run shorter.
What about cold weather?
Low temperatures reduce available capacity. Allow extra margin for cold conditions.
How do I use the Battery Runtime Calculator?
Enter the required values for Battery capacity, Battery voltage, Load power, Usable depth of discharge, Inverter / converter efficiency. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.
What formula does the Battery Runtime Calculator use?
Runtime (h) = Capacity (Ah) × Voltage (V) × DoD × Efficiency ÷ Load (W). The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.
Can the Battery Runtime Calculator be used for exact decisions?
Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.
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Calculate resistance step by step: R = V ÷ I, or for a conductor R = ρ × L ÷ A (A in m²).