Battery capacity in amp-hours does not translate directly to running time, because you never use the full rated capacity and the inverter converting DC to AC loses some of it along the way. Here is what a common battery bank actually delivers running a electric fireplace.
A 12V 100Ah battery, discharged to 80 percent and run through an inverter at 90 percent efficiency, delivers about 864 usable watt-hours. A electric fireplace at 1,500 W would run for roughly 0.6 hours on that battery alone.
Runtime for your own electric fireplace
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Planning estimate. The rate box is prefilled with a regional average; the figure on your own bill is the one that matters. Power is draw while running, not while switched on.
Why usable capacity is well below the rated number
A 100Ah battery does not give you 100Ah of usable energy. Two losses apply before the appliance sees any power. Depth of discharge limits how far you can drain the battery without shortening its life: lead-acid batteries are typically limited to 50 percent, while LiFePO4 packs are commonly rated for 80 percent or more. Then the inverter converting battery DC to household AC loses roughly 10 percent to heat.
Multiply those together and a 100Ah 12V lead-acid battery at 50 percent depth of discharge delivers about 540 usable watt-hours, while the same battery in LiFePO4 at 80 percent delivers about 864. That difference alone changes runtime by 60 percent on an identical-looking battery.
Runtime by depth of discharge
| Depth of discharge | Runtime on 100Ah 12V |
|---|---|
| 50% | 0.4 hours |
| 60% | 0.4 hours |
| 80% (typical LiFePO4) | 0.6 hours |
| 100% (lead-acid, not recommended) | 0.7 hours |
Running a lead-acid battery past 50 percent regularly shortens its life sharply, which is why the 100 percent row above is marked not recommended. LiFePO4 tolerates deeper cycling and is why most new battery banks are specified that way now.
Runtime by battery bank size
| Bank | Capacity | Runtime |
|---|---|---|
| 12V 50Ah | 0.60 kWh | 17 minutes |
| 12V 100Ah | 1.20 kWh | 35 minutes |
| 12V 200Ah | 2.40 kWh | 1.2 hours |
| 24V 100Ah | 2.40 kWh | 1.2 hours |
| 48V 100Ah | 4.80 kWh | 2.3 hours |
| 48V 280Ah | 13.44 kWh | 6.5 hours |
Higher voltage banks at the same Ah rating store proportionally more energy, which is why a 48V 100Ah bank runs a load four times longer than a 12V 100Ah bank of the same amp-hour rating. Voltage and amp-hours are not directly comparable without doing that multiplication.
Sizing a battery to run it for a full day
Running this appliance for its typical 5 hours a day needs about 7.50 kWh delivered, which works out to roughly 868 Ah at 12V once depth of discharge and inverter losses are included. That is the number to size against if the goal is running it through an outage rather than for a fixed window.
For multi-day autonomy, multiply by the number of days and add margin for a cloudy stretch if the bank is charged by solar. Undersizing here is the most common mistake in off-grid and backup planning: people size for the appliance running once, not for it running every day the outage lasts.
Solar to recharge the bank
7.50 kWh of daily use, the amount this appliance draws in 5 hours, needs roughly 6 standard 400 W solar panels to recharge in a single day of average sun, before accounting for anything else the bank is asked to run. A battery with no way to recharge is simply a finite store that runs out, so pairing capacity with generation is what makes a system self-sustaining rather than a one-time buffer.
Full array, inverter and panel-count detail for this specific appliance is on the solar sizing page, which uses the same load figures as this page.