Battery Runtime Calculator
Portable power stations and battery banks are a quiet, fume-free alternative or companion to a generator. This calculator estimates how long a battery will run your devices from its capacity, its chemistry and the load you connect.
Battery Runtime Calculator
Estimate how long a battery bank or portable power station can run your devices.
Real runtime varies with temperature, battery age, discharge rate and inverter idle draw. Lead-acid capacity drops noticeably at high discharge rates.
The formula
Runtime (hours) = capacity (Wh) × usable depth of discharge × inverter efficiency ÷ load (W)
- Capacity in Wh: power stations list this directly. For a battery rated in amp-hours, multiply by voltage: 100 Ah × 12 V = 1,200 Wh.
- Usable depth of discharge: lithium iron phosphate (LiFePO4) batteries and most power stations can safely deliver about 90% of their rating. Lead-acid batteries should not be discharged below about 50% if you want them to last.
- Inverter efficiency: converting battery DC to 120 V AC typically loses 10 to 15%. Use 100% for 12 V DC devices plugged into DC ports.
Worked examples
- A 2,000 Wh power station running a 300 W load: 2,000 × 0.9 × 0.9 ÷ 300 = 5.4 hours (5 hr 24 min).
- A 100 Ah 12 V AGM battery running a 100 W load through an inverter: 1,200 × 0.5 × 0.9 ÷ 100 = 5.4 hours.
Typical runtimes on a 1,000 Wh power station
| Device | Typical draw | Approximate runtime |
|---|---|---|
| Wi-Fi router and modem | 25 W | 32 hours |
| Laptop | 60 W | 13.5 hours |
| CPAP machine (no humidifier) | 40 W | 20 hours |
| Full-size refrigerator (average including cycling) | 150 W | 5.4 hours |
| 55-inch LED TV | 120 W | 6.8 hours |
| 1,000 W microwave | 1,000 W | 49 minutes |
Calculated with 90% usable capacity and 90% inverter efficiency. A refrigerator’s compressor cycles on and off, so its average draw is much lower than its running watts; the power station must still be able to supply the starting surge.
Battery or generator?
Batteries are silent, safe indoors and need no fuel, but their energy is limited. A 2 kWh power station holds roughly the energy a 7,500 W gasoline generator produces in under an hour at half load. Many households combine both: a battery for overnight quiet hours and electronics, and a generator for heavy loads and recharging. Compare running costs with the fuel consumption calculator.
Frequently asked questions
Why is my real runtime shorter than the estimate?
Cold temperatures, older batteries, high discharge rates and the inverter’s own idle draw (often 10 to 30 W) all reduce runtime. Lead-acid batteries lose a significant share of capacity when discharged quickly.
Can I recharge a power station with a generator?
Yes. Plug the power station’s AC charger into the generator. An inverter generator is the best choice because its clean output suits the charger electronics.