Batteries2 min read
A battery that is too small runs flat in the middle of a cut; one that is too big costs more than it needs to. Three questions get you to the right size.
1. What must keep running?
List only the essentials and add up their watts. For example: 4 fans at 75 W, 4 LED lights at 10 W and a TV at 100 W comes to 440 W.
2. For how many hours?
Think about your longest regular power cut. If cuts usually last up to 3 hours, plan for 3 hours of backup.
3. Work out the battery size
Multiply load by hours: 440 W × 3 hours = 1,320 Wh. A 12 V battery gives about 80% of its rating in practice, so divide by 12 × 0.8 = 9.6. That gives about 138 Ah, so a 150 Ah battery suits this home.
The inverter needs a VA rating above your load. Divide watts by 0.8: 440 W needs at least 550 VA, so a 700–900 VA inverter leaves some headroom.
Tubular or flat plate?
- Tubular batteries cost more but last longer and handle frequent, long cuts well
- Flat plate batteries are cheaper and suit short, occasional cuts
- Both need their water level checked and topped up as the manufacturer recommends
Keep the battery in a well-ventilated spot, away from direct sun, and never top it up with tap water.
