Electrical Calculator
Battery Runtime Calculator
Estimate battery runtime using battery voltage, battery capacity, and load power.
What this calculator does
This calculator gives a simple estimate of how long a battery may run a load based on battery voltage, battery capacity, and load power.
It is useful for quick checks involving UPS backup time, solar battery systems, 12V or 24V battery setups, portable power systems, and basic backup planning.
Inputs
Result
How to read the result
The result is a theoretical runtime based on simple energy conversion. In real use, the actual runtime may be shorter due to inverter losses, battery aging, depth of discharge limits, temperature, cable losses, and load variation.
In other words, this result is best treated as a quick estimate, not a guaranteed operating time.
Formula
Battery Energy (Wh) = Battery Voltage (V) × Battery Capacity (Ah)
Runtime (Hours) = Battery Energy (Wh) ÷ Load Power (W)
Example
If battery voltage is 12V, battery capacity is 100Ah, and load power is 120W:
Battery Energy = 12 × 100 = 1200 Wh
Runtime = 1200 ÷ 120 = 10 hours
Important notes
Real runtime is usually lower
Many systems do not deliver the full theoretical battery energy to the load. Efficiency losses and battery condition matter.
Battery capacity depends on discharge conditions
A battery rated at a certain Ah value may not deliver exactly that capacity under all load conditions.
This is not a full battery sizing tool
This page is intended for quick runtime estimation, not detailed battery system design or protection planning.
FAQ
Is this runtime exact?
No. This is a simple estimate. Real runtime may be lower depending on battery condition, inverter losses, discharge efficiency, and temperature.
What does Ah mean?
Ah stands for ampere-hour, which represents battery capacity.
Can I use this for UPS or solar battery estimates?
Yes. It can be used as a quick estimate for UPS, solar, or backup battery usage.
Why does real runtime often differ from the result?
Real systems include efficiency losses, battery aging, discharge limits, and operating conditions that reduce usable runtime.