How much lithium battery backup does your home need?
Size the battery from what you actually run during a power cut, not from the shop's biggest model.
Step 1: list what must run during a cut
| Appliance | Typical power | Quantity | Total |
|---|---|---|---|
| Ceiling fan (BLDC) | 30 W | 3 | 90 W |
| LED light | 10 W | 5 | 50 W |
| Wi-Fi router | 10 W | 1 | 10 W |
| LED TV | 60 W | 1 | 60 W |
| Total running load | 210 W | ||
Older ceiling fans use about 70–75 W each. Check the label on your appliances.
Step 2: multiply by hours of backup
Energy needed = load × hours. For 210 W over 4 hours: 210 × 4 = 840 Wh.
Step 3: allow for inverter losses
Inverters lose some energy in conversion. Divide by about 0.85–0.9 to be safe: 840 ÷ 0.85 ≈ 990 Wh, or roughly 1 kWh.
Step 4: pick the battery
LiFePO4 batteries can be used down to a much lower charge level than lead-acid, so most of the rated capacity is usable. In this example, a battery of about 1.2 kWh gives around 4 hours for these loads.
| Running load | ~3 hours | ~6 hours | ~12 hours |
|---|---|---|---|
| 200 W | ~0.7 kWh | ~1.4 kWh | ~2.8 kWh |
| 400 W | ~1.4 kWh | ~2.8 kWh | ~5.6 kWh |
| 800 W | ~2.8 kWh | ~5.6 kWh | ~11 kWh |
Rounded estimates including about 15% inverter loss. Your installer should confirm the size.
What about the fridge and mixer?
A fridge motor and a mixer grinder draw a high current for a moment when they start. The battery may have enough energy, but the inverter must also be rated for that starting surge. Tell your installer about these loads.
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