How Long Will It Last?
Runtime by Battery Size (Lithium, AC Output)
| Load | Watts | 500 Wh | 1,000 Wh | 2,000 Wh | 5,000 Wh |
|---|---|---|---|---|---|
| Phone charging | 10 W | 38 h | 76 h | 153 h | 382 h |
| LED work light | 20 W | 19 h | 38 h | 76 h | 191 h |
| Wi-Fi router + modem | 15 W | 26 h | 51 h | 102 h | 255 h |
| CPAP (no humidifier) | 40 W | 9.6 h | 19 h | 38 h | 96 h |
| Laptop | 60 W | 6.4 h | 13 h | 26 h | 64 h |
| Mini fridge | 60 W | 6.4 h | 13 h | 26 h | 64 h |
| Full-size refrigerator (avg. cycling) | 150 W | 2.5 h | 5.1 h | 10 h | 26 h |
| 55" TV | 100 W | 3.8 h | 7.7 h | 15 h | 38 h |
| Tool battery charger | 100 W | 3.8 h | 7.7 h | 15 h | 38 h |
| Circular saw (while cutting) | 1,400 W | 0.3 h | 0.5 h | 1.1 h | 2.7 h |
| Coffee maker | 1,000 W | 0.4 h | 0.8 h | 1.5 h | 3.8 h |
| Space heater (low) | 750 W | 0.5 h | 1.0 h | 2.0 h | 5.1 h |
Assumes 90% usable capacity and 85% inverter efficiency. A load still needs to fit under the power station's continuous output rating: a 500 Wh unit rated for 300 W cannot run a 1,400 W saw at all.
The Battery Runtime Formula
Runtime (hours) = Battery Wh × Usable fraction × Efficiency ÷ Load watts
If your battery is rated in amp-hours, convert first: Wh = Ah × Volts. A 100 Ah, 12 V battery holds 1,200 Wh. Then knock off what you can't or shouldn't use, and what the inverter burns turning DC into AC.
Example: a 100 Ah 12 V LiFePO4 battery (1,200 Wh) running a 150 W load through an inverter: 1,200 × 0.9 × 0.85 ÷ 150 = about 6.1 hours. The same size lead-acid battery, where you should only use half, gives about 3.4 hours.
Usable Capacity: Lithium vs Lead-Acid
Lead-acid and AGM batteries last far longer if you stop at about 50% depth of discharge, so only half the label capacity is really yours. LiFePO4 handles 80–100% depth of discharge for thousands of cycles. That's why a 100 Ah lithium battery does the work of roughly two 100 Ah lead-acid batteries. Portable power stations list their capacity in Wh and already protect the cells, so 85–90% usable is a fair planning number.
Inverter Losses
Plugging into the AC outlet runs power through an inverter that converts 12 V or 48 V DC into 120 V AC. Good inverters are 85–92% efficient, and they draw a little power just being switched on, often 10–30 W idle on larger units. Running DC devices from the 12 V or USB ports skips most of that loss. Turn the AC inverter off when you only need USB charging.
Surge and Continuous Ratings
Capacity tells you how long; the output rating tells you whether it will run at all. A circular saw might pull 1,400 W while cutting and twice that for a split second at start. The power station needs a continuous rating above the running draw and a surge rating above the start. Check both before you count on a battery for jobsite tools. For bigger loads, see the generator sizing calculator.
Real-World Factors
Cycling loads: a refrigerator's compressor is only on part of the time. Use its average draw (roughly 100–200 W for a modern full-size fridge), not its rated amps. Cold weather: lithium and lead-acid both deliver less below freezing, and most lithium batteries won't charge below 32°F. High discharge rates: lead-acid loses noticeable capacity at heavy loads (Peukert effect), so a 100 Ah AGM delivers fewer amp-hours at 50 A than at 5 A. Age: plan on 80% of original capacity after a few hundred cycles for lead-acid or a few thousand for LiFePO4.
Recharging
Recharge time is capacity divided by charge rate, plus 10–20% for losses. A 1,000 Wh station on a 200 W solar panel in good sun needs about 6 hours; on a 600 W wall charger, closer to 2 hours.
Frequently Asked Questions
A 12 V 100 Ah battery holds 1,200 Wh. Running a 100 W load through an inverter, a lithium battery lasts about 9 hours and a lead-acid battery about 5 hours, because you should only use half of a lead-acid battery.
Usually about 5–8 hours. A full-size fridge averages roughly 100–150 W once you account for the compressor cycling off. Check that the station can handle the compressor start surge, often 1,000–2,000 W.
Multiply amp-hours by the battery voltage. 100 Ah at 12 V is 1,200 Wh. 50 Ah at 48 V is 2,400 Wh.
Inverter losses, the inverter idle draw, cold temperatures, and loads that pull more than their label are the usual causes. Running devices from DC or USB ports instead of the AC outlet helps.
Yes, if its continuous output exceeds the tool’s running watts and its surge rating covers the start. A 2,000 W station can run a circular saw; runtime under that load is short, often 30–60 minutes of cutting on 1,000–2,000 Wh.
