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A Laptop draws about 65W, so a 150Ah 12V tubular battery runs one of them for roughly 9 hours 42 minutes on its own. That comes from 630Wh usable energy divided by 65W. A mainstream laptop with its charger connected.
A mainstream laptop with its charger connected. The 65W figure used across this page is a typical mid-range Indian retail unit — check the nameplate on yours and put the real number into the calculator, because a 10W difference on an appliance you run for six hours is 60Wh out of a budget of only a few hundred.
Category: Work. People search for this as laptop charger watts, notebook power — all the same question, and all answered by the same arithmetic.
Usable energy is Ah x 12V x 0.7 efficiency x 0.5 depth of discharge. Divide that by the appliance draw and you have the runtime with nothing else connected.
| Battery | Usable energy | Runtime with one unit | Runtime with two |
|---|---|---|---|
| 100Ah | 420Wh | 6 hours 28 minutes | 3 hours 14 minutes |
| 120Ah | 504Wh | 7 hours 45 minutes | 3 hours 53 minutes |
| 135Ah | 567Wh | 8 hours 43 minutes | 4 hours 22 minutes |
| 150Ah | 630Wh | 9 hours 42 minutes | 4 hours 51 minutes |
| 165Ah | 693Wh | 10 hours 40 minutes | 5 hours 20 minutes |
| 180Ah | 756Wh | 11 hours 38 minutes | 5 hours 49 minutes |
| 200Ah | 840Wh | 12 hours 55 minutes | 6 hours 28 minutes |
| 220Ah | 924Wh | 14 hours 13 minutes | 7 hours 6 minutes |
| 250Ah | 1050Wh | 16 hours 9 minutes | 8 hours 5 minutes |
Nothing stops you connecting more units — the limit is runtime, not the inverter, until you hit the surge ceiling below.
| Quantity | Continuous draw | Runtime | Band |
|---|---|---|---|
| 1 | 65W | 9 hours 42 minutes | Low load |
| 2 | 130W | 4 hours 51 minutes | Moderate |
| 3 | 195W | 3 hours 14 minutes | Moderate |
| 4 | 260W | 2 hours 25 minutes | Moderate |
| 5 | 325W | 1 hour 56 minutes | High load |
| 6 | 390W | 1 hour 37 minutes | High load |
Very few appliances run flat out for a full hour. A fridge compressor cycles, a mixer runs in bursts, a pump fills a tank and stops. Battery Buddy asks for minutes run per hour and multiplies the wattage by that fraction — which is why its answers are usually longer, and more honest, than a calculator that assumes continuous draw.
| Minutes run per hour | Average hourly draw | Runtime on a 150Ah battery |
|---|---|---|
| 15 min | 16.3W | 38 hours 46 minutes |
| 30 min | 32.5W | 19 hours 23 minutes |
| 40 min | 43.3W | 14 hours 32 minutes |
| 45 min | 48.8W | 12 hours 55 minutes |
| 60 min | 65W | 9 hours 42 minutes |
A Laptop is electronically well behaved: Battery Buddy applies a 1.2x start-up multiplier, so one unit peaks at roughly 78W. It is the motor loads on the same inverter, not this one, that will trip you.
Peak demand = total continuous load + the single largest start-up surge. The sizing advisor runs that check automatically for whatever mix you enter.
These are complete household and shop profiles we model, each with its own worked page.
| Profile | Average draw | Backup on a 150Ah battery |
|---|---|---|
| Laptop + WiFi router + 1 fan + 2 lights | 163W | 3 hours 52 minutes |
About 65W while running. A mainstream laptop with its charger connected. Always confirm against the nameplate rating on your own unit before sizing a battery around it.
Roughly 9 hours 42 minutes with nothing else connected: 630Wh usable divided by 65W. Add anything else to the inverter and that time drops proportionally.
Battery Buddy applies a 1.2x multiplier, so a single unit peaks near 78W at switch-on before settling to 65W. That is a mild spike, so it rarely causes an overload on its own.
Yes — one unit runs about 6 hours 28 minutes on a 100Ah 12V battery at 70% efficiency. Whether that is enough depends on how long your outages actually last and what else shares the inverter.
The figures assume 70% system efficiency. An older battery, low electrolyte, corroded terminals or thin cabling all reduce the effective factor. Measure yours with the efficiency estimator and re-run the numbers — it takes one discharge test.
Battery Buddy is free, needs no sign-up, sells no batteries and shows every formula it uses. It is built by Flocci Technologies, an India-first AI-native software studio behind 30+ apps that share one Flocci identity.