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A Set-Top Box draws about 15W, so a 150Ah 12V tubular battery runs one of them for roughly 42 hours on its own. That comes from 630Wh usable energy divided by 15W. Small but constant — a set-top box draws power whenever the TV is on.
Small but constant — a set-top box draws power whenever the TV is on. The 15W 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: Entertainment. People search for this as dth box, cable box watts — 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 | 28 hours | 14 hours |
| 120Ah | 504Wh | 33 hours 36 minutes | 16 hours 48 minutes |
| 135Ah | 567Wh | 37 hours 48 minutes | 18 hours 54 minutes |
| 150Ah | 630Wh | 42 hours | 21 hours |
| 165Ah | 693Wh | 46 hours 12 minutes | 23 hours 6 minutes |
| 180Ah | 756Wh | 50 hours 24 minutes | 25 hours 12 minutes |
| 200Ah | 840Wh | 56 hours | 28 hours |
| 220Ah | 924Wh | 61 hours 36 minutes | 30 hours 48 minutes |
| 250Ah | 1050Wh | 70 hours | 35 hours |
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 | 15W | 42 hours | Low load |
| 2 | 30W | 21 hours | Low load |
| 3 | 45W | 14 hours | Low load |
| 4 | 60W | 10 hours 30 minutes | Low load |
| 5 | 75W | 8 hours 24 minutes | Low load |
| 6 | 90W | 7 hours | Low 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 | 3.8W | 168 hours |
| 30 min | 7.5W | 84 hours |
| 40 min | 10W | 63 hours |
| 45 min | 11.3W | 56 hours |
| 60 min | 15W | 42 hours |
A Set-Top Box is electronically well behaved: Battery Buddy applies a 1.2x start-up multiplier, so one unit peaks at roughly 18W. 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 |
|---|---|---|
| TV + set-top box + 2 fans + 3 lights | 242W | 2 hours 36 minutes |
About 15W while running. Small but constant — a set-top box draws power whenever the TV is on. Always confirm against the nameplate rating on your own unit before sizing a battery around it.
Roughly 42 hours with nothing else connected: 630Wh usable divided by 15W. Add anything else to the inverter and that time drops proportionally.
Battery Buddy applies a 1.2x multiplier, so a single unit peaks near 18W at switch-on before settling to 15W. That is a mild spike, so it rarely causes an overload on its own.
Yes — one unit runs about 28 hours 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.