Inverter battery backup time chart
Backup time for one 12 V tubular battery at common household loads, with 85% inverter efficiency and the inverter cutting off at about 85% discharge. For a 24 V inverter with two batteries, roughly double the time.
| Load | 100 Ah | 150 Ah | 200 Ah | 220 Ah |
|---|---|---|---|---|
| 100 W | 7 h 20 min | 12 h 10 min | 17 h 20 min | 19 h 4 min |
| 200 W | 3 h 5 min | 5 h 7 min | 7 h 20 min | 8 h 15 min |
| 300 W | 1 h 51 min | 3 h 5 min | 4 h 25 min | 4 h 58 min |
| 500 W | 59 min | 1 h 38 min | 2 h 20 min | 2 h 38 min |
| 800 W | 33 min | 54 min | 1 h 18 min | 1 h 28 min |
150Ah battery backup time
A 150 Ah tubular battery is the most common size for home inverters. One battery on a 12 V inverter stores 1.8 kWh; two on a 24 V inverter store 3.6 kWh. At 500 W, one 150 Ah battery gives about 1 h 38 min of backup, and two give about 3 h 52 min.
| Load | 1 × 150 Ah (12 V) | 2 × 150 Ah (24 V) |
|---|---|---|
| 100 W | 12 h 10 min | 26 h 1 min |
| 200 W | 5 h 7 min | 12 h 10 min |
| 300 W | 3 h 5 min | 7 h 20 min |
| 400 W | 2 h 9 min | 5 h 7 min |
| 500 W | 1 h 38 min | 3 h 52 min |
| 600 W | 1 h 18 min | 3 h 5 min |
| 800 W | 54 min | 2 h 9 min |
| 1000 W | 41 min | 1 h 38 min |
200Ah battery backup time
A 200 Ah battery stores a third more energy than a 150 Ah one, but at 500 W its backup is about 43% longer, because a bigger battery is drained more gently and loses less to Peukert’s law. At 500 W, one 200 Ah battery gives about 2 h 20 min, and two on a 24 V inverter about 5 h 33 min.
| Load | 1 × 200 Ah (12 V) | 2 × 200 Ah (24 V) |
|---|---|---|
| 100 W | 17 h 20 min | 34 h 41 min |
| 200 W | 7 h 20 min | 17 h 20 min |
| 300 W | 4 h 25 min | 10 h 30 min |
| 400 W | 3 h 5 min | 7 h 20 min |
| 500 W | 2 h 20 min | 5 h 33 min |
| 600 W | 1 h 51 min | 4 h 25 min |
| 800 W | 1 h 18 min | 3 h 5 min |
| 1000 W | 59 min | 2 h 20 min |
Battery backup time formula
Backup (h) = Ah × V × number of batteries × efficiency ÷ load (W)
This is the formula most battery shops use, often with a single 0.8 factor for efficiency. For 150 Ah and 250 W it gives 5.8 hours. The calculator above goes two steps further:
- Inverter cut-off. The inverter switches off when the battery voltage falls to around 10.5 V, before the battery is completely empty, so we count about 85% of its capacity.
- Peukert’s law. Lead-acid batteries are rated over 20 hours. Drained in 4 or 5 hours they deliver noticeably less, so backup at higher loads is shorter than the simple formula suggests.
Both effects together explain why the calculator shows 3 h 52 min instead of 5.8 hours. If your battery is a few years old, lower battery health in Advanced settings as well. The details are in how battery runtime is calculated.
Typical power use of home appliances
| Appliance | Typical watts |
|---|---|
| Ceiling fan (standard) | 70–80 W |
| Ceiling fan (BLDC) | 28–35 W |
| LED bulb | 7–12 W |
| LED tube light | 18–22 W |
| LED TV (32–43 inch) | 40–80 W |
| Wi-Fi router | 6–12 W |
| Laptop charging | 45–90 W |
| Refrigerator (average over a day) | 40–80 W |
| Desktop computer with monitor | 150–250 W |
Check the rating label for your own appliances. Air conditioners, geysers, irons and microwaves draw 1,000–2,000 W and are not suitable for a typical home inverter.
Tips to get longer backup
- Switch to BLDC fans and LED lights: they cut the load by more than half.
- Keep tubular battery water topped up with distilled water and the terminals clean.
- Make sure the battery reaches full charge between power cuts; a battery that never fully charges loses capacity.
- For daily long cuts, size the battery properly with the battery size calculator, or add solar charging.