What size inverter and battery does a two-bedroom flat need?

The load this premises actually carries

Two bedrooms plus a hall, with the fridge kept alive through daytime cuts. 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.

Why 800VA and not something bigger

Inverters are sold in VA, not watts. Battery Buddy converts with the standard power factor of 0.8 and adds a 25% safety margin: (434W / 0.8) x 1.25 = 678VA, which rounds up to the 800VA 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.

Why the system runs at 24V

Medium loads with improved efficiency. Typically two 12V batteries in series. Battery Buddy escalates system voltage automatically once average load passes 400W (to 24V), 800W (to 48V) and 2000W (to 96V). At 434W this profile sits at 24V.

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 — 2 x 220Ah 12V batteries in series.

Battery bank and charging

Target energy is 434W x 4 hours = 1736Wh. Dividing by 24V x 0.7 efficiency x 0.5 depth of discharge gives 207Ah, and the nearest standard bank is 220Ah — rated for a sustained load of 560-750W.

Charge it at 22-27A, 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 4-hour target with room to spare — roughly 4 hours 15 minutes at the assumed efficiency.

The overload check nobody runs

With everything on, continuous draw is 484W. The Refrigerator (190L) spikes to about 450W at start-up, so peak demand is 934W. A 800VA inverter does NOT hold that — expect an overload beep the moment the Refrigerator (190L) starts. Move up a VA tier or keep that appliance off the inverter circuit.

Backup target versus battery cost

Every extra hour of backup is bought with amp-hours. This is the trade-off for exactly this load.

Frequently asked questions

What size inverter is needed for a two-bedroom flat?

A 800VA inverter for a 434W average load. That comes from (434 / 0.8) x 1.25 = 678VA, rounded up to the nearest standard retail size.

What battery capacity does a two-bedroom flat need for 4 hours of backup?

About 207Ah at 24V, which maps to a standard 220Ah bank — 2 x 220Ah 12V batteries in series. The energy target is 1736Wh at 70% efficiency and 50% depth of discharge.

Should this run on 12V or a higher system voltage?

24V. Medium loads with improved efficiency. Typically two 12V batteries in series. The threshold Battery Buddy uses is 400W average load for 24V, 800W for 48V and 2000W for 96V.

What charging current should the inverter provide?

22-27A, following the C/10 to C/8 guideline for a 220Ah lead-acid bank. Too little current never completes a cycle in short grid windows; too much cooks the electrolyte.

Will the inverter trip when a motor starts?

Peak demand here is 934W — 484W continuous plus the 450W start-up surge of the Refrigerator (190L). A 800VA inverter does not clear it, so size up or move that appliance off the inverter.

Is this a brand recommendation?

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.