Battery Run Time Calculator
Estimate how long your battery will last based on voltage, amp-hours, load in watts, inverter efficiency, and depth of discharge. This is one of the fastest ways to estimate backup battery runtime during a power outage.
12V / 24V / 48V Lead-acid or LiFePO4 Runtime in hours + minutes Usable watt-hours shown
Enter Your Battery and Load
Most small backup batteries are 12V. Larger systems may be 24V or 48V.
Example: 100Ah battery.
Enter the device or combined load you want to power.
Use 90% as a realistic starting point for many inverter setups.
LiFePO4 often uses higher discharge. Lead-acid is commonly limited to around 50%.
Presets auto-adjust inverter efficiency and depth of discharge.
Quick Load Examples
Battery watt-hours = Volts × Amp-hours
Usable watt-hours = Battery watt-hours × Inverter efficiency × Depth of discharge
Estimated runtime = Usable watt-hours ÷ Load watts This calculator gives an estimate. Real-world runtime can be lower due to startup surges, inverter losses, battery age, temperature, discharge curve, and manufacturer limits.
Your Estimated Runtime
Estimated Runtime
8h 38m
8.64 hours total runtime
Usable Energy
864 Wh
Total battery energy: 1200 Wh before losses and discharge limits
Setup Summary
12V × 100Ah ÷ 100W
Using 90% inverter efficiency and 80% depth of discharge
Common Battery Runtime Examples
| Battery | Load | Rough Runtime |
|---|---|---|
| 12V 100Ah | 100W | ~8 to 9 hours |
| 12V 100Ah | 600W | ~1.4 hours |
| 12V 200Ah | 100W | ~17 hours |
| 24V 100Ah | 300W | ~5.8 hours |
Important Notes
- Square footage does not determine battery runtime. Your actual load does.
- Motor-driven devices like refrigerators and pumps often have startup surges.
- Lead-acid batteries should usually not be drained as deeply as LiFePO4.
- For outage planning, always leave yourself margin instead of sizing too tightly.
- If you need to run major household loads, a generator or larger battery system may make more sense.
Planning a Bigger Backup Power Setup?
Compare generators, battery backup options, and home backup gear to find the right fit for your outage plan.
Compare Backup Power Options