Estimate battery backup time
Battery capacity in amp-hours multiplied by voltage gives an approximate energy capacity in watt-hours. Apply your usable-efficiency percentage, then divide by the load in watts to estimate hours.
For 100 Ah at 12 V, 80% usable efficiency and a 300 W load, the result is 3.2 hours. This energy model does not simulate battery aging, discharge-rate effects or temperature.
What is this calculator?
Estimate runtime from battery capacity, voltage and power consumption.
What can you use it for?
Use it for practical planning, conversions, measurement or checking the result described here. Estimate runtime from battery capacity, voltage and power consumption.
How to use it
- Enter battery capacity (ah).
- Enter voltage (v).
- Enter load (w).
- Enter usable efficiency (%).
- Select Calculate (or Generate for random tools).
- Read the answer and any additional results below the form. Check the units and the limits of the method.
Formula and method
The formula uses the units and definitions shown above. Each input is substituted before the arithmetic is evaluated; the calculated output is rounded for display.
Worked example
Battery capacity (Ah): 100, Voltage (V): 12, Load (W): 300, Usable efficiency (%): 80. The result is 3.2 hours (result).
Assumptions and limits
Simplified energy model. Discharge rate, aging and temperature affect actual runtime.
Frequently asked questions
What inputs does the Battery Runtime Calculator need?
Use battery capacity (ah), voltage (v), load (w), usable efficiency (%). Read the answer and any additional results below the form. Check the units and the limits of the method.
What assumptions apply to the Battery Runtime Calculator?
Simplified energy model. Discharge rate, aging and temperature affect actual runtime.