How to Use the Battery Runtime Calculator
Simply dividing capacity by load current overstates how long a battery will actually last. Real batteries lose lifespan fast if you drain them completely, so you need to apply a depth of discharge (DoD) limit, and you also need to account for power lost in the inverter and wiring to get an estimate that matches reality.
This calculator takes battery capacity (Ah), your actual load current (A), depth of discharge (%), and system efficiency (%) and returns both the usable capacity and the estimated runtime. Lithium batteries commonly use an 80-90% DoD, while lead-acid batteries are often kept closer to 50%; efficiency is typically set around 85% to account for inverter and wiring losses.
Use it to estimate runtime for camping power banks, backup power systems, or small solar battery banks. If your battery is rated in mAh, divide by 1,000 to convert to Ah before entering it.
Frequently Asked Questions
Fully draining a lithium battery shortens its lifespan, so 80-90% is a common practical limit. Lead-acid batteries are often limited to around 50%.
It accounts for losses in the inverter and wiring between the battery and the load, so actual runtime is shorter than the theoretical value.
Divide by 1,000 to convert to Ah before entering it. For example, 3,000mAh becomes 3Ah.