How Much Battery Do I Need for Backup?
Battery size = your load × backup hours ÷ (voltage × depth of discharge × efficiency). A home pulling about 400W that wants 2 hours of backup needs a 12V 110Ah battery. Use the table below as a starting point, then check your exact appliances in the battery calculator.
Quick reference: load → battery size (2 hours of backup)
| Your load | Example | Battery |
|---|---|---|
| 200W | 2 fans + 4 bulbs + router | 12V 55Ah |
| 400W | 4 fans + 6 bulbs + TV + router + CCTV | 12V 110Ah |
| 600W | + refrigerator | 12V 165Ah |
| 800W | + refrigerator + pump (running) | 12V 220Ah |
| 1000W | Large home / small shop | 24V 150Ah |
Rounded up to commonly available sizes. Larger loads step up to 24V/48V systems automatically in the calculator — thinner cables, same energy.
How long will a battery run my load?
Estimated backup time
≈ 2.8 hours
150Ah 12V battery at 400W load, using typical discharge and efficiency assumptions.
Based on an 80% depth of discharge and typical inverter (90%) and battery (85%) efficiencies — the same assumptions used across this calculator. Real results vary with battery age and temperature.
Why 12V, 24V or 48V?
Small home systems (up to about 130Ah at 12V) use 12V — it's the most common battery size in Bangladesh, the cheapest, and the easiest to maintain. As the required capacity grows, 24V or 48V systems carry the same power with half or a quarter of the current, which means thinner cables and smaller losses. You don't need to choose — the calculator picks the most practical voltage for your numbers.
Size it for your own home
Add your appliances and backup hours to the battery backup calculator — it returns a practical size (not a theoretical number) and an alternative, one step bigger, for extra reserve.
Frequently asked questions
How long will a 150Ah battery run my home?
A 12V 150Ah battery stores about 1.5kWh of usable energy after discharge limits. At a 400W load that's roughly 2.5–3 hours; at 150W (just a fridge and lights) it can run 6–7 hours. Use the calculator on this page with your actual load for a precise answer.
How many watts is a 150Ah battery?
A 12V 150Ah battery stores 1800Wh (1.8kWh) of total energy, of which about 1.4–1.5kWh is usable before you should recharge. Watts aren't stored — energy is — so think of it as 1.5kWh of capacity, not a wattage rating.
Can a 150Ah battery run a refrigerator?
Yes. A fridge runs at about 150W, so a 12V 150Ah battery delivers roughly 7 hours of backup for it. Just make sure the IPS has a good surge rating for the compressor's startup draw.
Tubular, flat plate or lithium — which battery should I buy?
For frequent, deep backup use in a Bangladeshi home, a tubular lead-acid battery is the usual recommendation — it survives deep discharge cycles best at a reasonable price. Lithium (LiFePO4) costs more but lasts longer and is lighter. The amp-hour size you need is the same either way; the type affects budget and lifespan.