Battery Runtime Calculator
Estimate battery runtime from capacity, voltage, and load, with depth-of-discharge and efficiency factors.
Processed locally in your browser — nothing is uploaded.
Battery Runtime Calculator
~50% for lead-acid, 80–90% for LiFePO4.
Inverter and wiring losses; ~90% is typical.
Results
- Estimated runtime
- 14h 24m
- Runtime (decimal hours)
- 14.4 h
- Usable energy
- 960 Wh
- Load
- 60 W
Real capacity shrinks at high discharge rates (Peukert effect), low temperatures, and with battery age — treat this as an upper-bound estimate.
About Battery Runtime Calculator
Multiply capacity by voltage for watt-hours, keep only the usable depth-of-discharge fraction, apply inverter efficiency, and divide by the load: that's the runtime this tool computes, shown in hours and minutes. Capacity can be entered in Ah or mAh and the load in watts or amps.
Common uses
- Estimate how long a 100 Ah LiFePO4 battery runs a 12 V fridge
- Size a power-station purchase for a CPAP machine or laptop
- Sanity-check a camper or boat house-battery plan
Example
Input
100 Ah · 12 V · 60 W load · 80% DoD · 90% efficiency
Output
≈ 14 h 24 m
Limitations
- High discharge rates, cold temperatures, and battery age all reduce real capacity (Peukert effect) — treat results as an upper bound.
Frequently asked questions
How do I calculate how long a battery will last?
Multiply capacity by voltage to get watt-hours, keep the usable depth-of-discharge fraction, apply inverter efficiency, and divide by the load in watts. A 100 Ah 12 V battery at 80% DoD and 90% efficiency runs a 60 W load about 14.4 hours.
What is depth of discharge?
Depth of discharge is the fraction of a battery's capacity you actually drain. Lead-acid batteries age quickly below about 50% DoD, while LiFePO4 comfortably tolerates 80 to 90%, so the chemistry changes how much of the rated capacity is really usable.
Does this calculator upload my battery specs anywhere?
No. The runtime math runs locally in your browser and none of the capacity, voltage, or load figures you enter are transmitted or stored.
Why does my battery die faster than the calculator predicts?
Real capacity shrinks with high discharge rates (the Peukert effect), cold temperatures, and battery age, none of which the linear formula models. Treat the result as an upper bound and leave margin for critical loads.
What is the difference between Ah and mAh?
They measure the same thing at different scales: 1 Ah equals 1000 mAh. Phone power banks are usually rated in mAh and larger deep-cycle batteries in Ah; the calculator accepts either unit directly.