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For a single-room studio running 163W average load for 5 hours, Battery Buddy sizes a 600VA inverter and a 200Ah battery bank at 12V — Single 200Ah 12V battery. The energy target is 815Wh, which needs 194Ah at 70% efficiency and 50% depth of discharge. Charge it at 20-25A.
One room, one fan, two lights and a laptop — a deliberately small, long-running setup. Each appliance is counted at the minutes it genuinely runs in an hour, not at full nameplate wattage for sixty minutes — that duty-cycle step is what separates a sizing you can trust from a dealer's round number.
| Appliance | Watts each | Qty | Minutes per hour | Average draw |
|---|---|---|---|---|
| Ceiling Fan | 70W | 1 | 60 min | 70W |
| LED Bulb | 9W | 2 | 60 min | 18W |
| Laptop | 65W | 1 | 60 min | 65W |
| WiFi Router | 10W | 1 | 60 min | 10W |
| Total average hourly load | 163W |
Inverters are sold in VA, not watts. Battery Buddy converts with the standard power factor of 0.8 and adds a 25% safety margin: (163W / 0.8) x 1.25 = 255VA, which rounds up to the 600VA tier actually sold in Indian retail.
Oversizing is not free. A larger inverter idles at a higher no-load draw, costs more, and tempts you to add load the battery cannot support. Size the inverter to the load, then size the battery to the outage.
Common for small loads and basic home backup. Usually a single 12V battery. Battery Buddy escalates system voltage automatically once average load passes 400W (to 24V), 800W (to 48V) and 2000W (to 96V). At 163W this profile sits at 12V.
Higher DC voltage carries the same power at lower current, which means less heat in the cabling and a safer install. The cost is that batteries must be added in matched series sets — Single 200Ah 12V battery.
Target energy is 163W x 5 hours = 815Wh. Dividing by 12V x 0.7 efficiency x 0.5 depth of discharge gives 194Ah, and the nearest standard bank is 200Ah — rated for a sustained load of 250-340W.
Charge it at 20-25A, the C/10 to C/8 guideline. Under-charging leaves a lead-acid bank permanently short of full and is one of the most common reasons backup quietly halves over two years.
This bank clears the 5-hour target with room to spare — roughly 5 hours 9 minutes at the assumed efficiency.
With everything on, continuous draw is 163W. The Ceiling Fan spikes to about 105W at start-up, so peak demand is 268W. A 600VA inverter holds that with 55% headroom.
Every extra hour of backup is bought with amp-hours. This is the trade-off for exactly this load.
| Backup target | Energy needed | Bank Ah required | Nearest retail bank |
|---|---|---|---|
| 2 hours | 326Wh | 78Ah | 100Ah at 12V |
| 3 hours | 489Wh | 116Ah | 150Ah at 12V |
| 4 hours | 652Wh | 155Ah | 180Ah at 12V |
| 5 hours | 815Wh | 194Ah | 200Ah at 12V |
| 6 hours | 978Wh | 233Ah | 220Ah at 12V |
| 8 hours | 1304Wh | 310Ah | 220Ah at 12V |
A 600VA inverter for a 163W average load. That comes from (163 / 0.8) x 1.25 = 255VA, rounded up to the nearest standard retail size.
About 194Ah at 12V, which maps to a standard 200Ah bank — Single 200Ah 12V battery. The energy target is 815Wh at 70% efficiency and 50% depth of discharge.
12V. Common for small loads and basic home backup. Usually a single 12V battery. The threshold Battery Buddy uses is 400W average load for 24V, 800W for 48V and 2000W for 96V.
20-25A, following the C/10 to C/8 guideline for a 200Ah lead-acid bank. Too little current never completes a cycle in short grid windows; too much cooks the electrolyte.
Peak demand here is 268W — 163W continuous plus the 105W start-up surge of the Ceiling Fan. A 600VA inverter clears it.
No. Battery Buddy is brand-neutral and free — it returns a VA rating, an Ah figure, a system voltage and a charger current, and shows the formula behind each. Take those four numbers to any dealer and compare quotes on equal terms.
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.