Which inverter do you actually need?

The conversation in an electrical shop runs the same way in every Indian city. How many fans, how many lights, a TV? The salesman does the arithmetic on the counter and names a number — nine hundred VA, one-fifty ampere-hour — and a household that has just spent a summer in the dark says yes, because the number sounds like enough.

It may well be enough. But nothing in that exchange asked the question that decides the outcome. How much you can run at once and how long you can run it are two separate numbers, bought as two separate things inside the same box, and the shop's question only sizes the first. Families discover the second at nine in the evening, forty minutes into a three-hour cut, when the inverter starts beeping and the fans stop.

The good news is that the missing number is not a mystery. It is how long power is out in your locality, how often, and at what hour — and unlike most things in this purchase, that is something you can look up rather than guess.

The two numbers, and what each one buys

An inverter system is two purchases sold as one. The inverter is a box of electronics that turns 12 volts of battery into 230 volts of household supply. The battery is the tank. They are rated in different units because they do different jobs, and confusing them is the most common and most expensive mistake in this market.

The inverter's rating — 700 VA, 900 VA, 1500 VA — is about how much you can switch on at the same moment. Cross it and the unit beeps, then trips. It says nothing at all about duration: a 1500 VA inverter with a small battery runs a heavy load for a very short time, which is exactly the wrong shape of system for an Indian power cut.

The battery's rating — 100 Ah, 150 Ah, 200 Ah — is the tank. It decides how long, and only how long. Two houses with identical inverters and different batteries have completely different evenings.

The pattern worth avoiding is the one the market pushes hardest: a generously sized inverter paired with the cheapest battery that fits the budget. It sells well because the inverter is the part with the brand name on it. It is backwards. In a place with long cuts, the battery is the purchase and the inverter is the accessory.

Step one: add up what you want running

Not everything in the house — only what you want alive during a cut. Write the list down, because the total is usually smaller than people fear and occasionally much larger.

A common Indian evening — four fans, six lights, a television and the router — comes to roughly 350 to 400 watts with conventional fans, and closer to 200 with BLDC ones. Add a fridge and you are at 550 W or so, with brief surges well above it.

To turn watts into the VA number the shop quotes, divide by about 0.8 and leave headroom for the surge: 400 W becomes about 500 VA, which sits comfortably inside a 700 or 900 VA unit. Most homes need far less inverter than they are sold.

One caution about the ratings themselves. VA figures in this market are optimistic, and the model name is marketing. The number that matters is the continuous output in watts on the specification sheet, which is usually a good deal lower than the VA on the carton.

Step two: how long it will actually last

A battery's ampere-hours at 12 volts give you its nominal store of energy — a 150 Ah battery holds about 1,800 watt-hours on paper. You will not get 1,800. The inverter loses some in the conversion, the battery loses some as heat, and a lead-acid battery that is regularly drained flat has a short and expensive life, so about half of what it holds is what you should plan to use.

Put those together and one line of arithmetic gives the honest answer: runtime in hours is roughly the battery's Ah, times 12, times 0.6, divided by your load in watts.

So a 150 Ah battery carrying a 400 W load gives about two and three-quarter hours. Drop the load to 200 W — fans and lights only, television off — and the same battery runs for five and a half. Which is the real lesson of the formula: what you switch on during a cut moves the answer as much as what you bought.

These are planning figures, not promises — a battery three years old delivers meaningfully less than the same battery new, and a hot room takes more off the top. Treat the table as the best case you will see in year one.

Step three: look up your own power cuts

Here is where most of this purchase goes wrong. Households size the battery against a remembered worst evening, or against what a neighbour bought, and neither is data. The question you need answered is narrow and specific: in your area, over the last few months, how long has the power actually been out, and at what time of day?

That is the question this site exists to answer. Community reports for more than a hundred and thirty cities carry the duration people recorded and the hour they filed, so you can look at your own area before you look at a price tag.

Read against the table above, the pattern usually sorts itself into one of three answers. Cuts of an hour or two, a few times a week: a 100 or 150 Ah battery is ample, and anything larger is money spent on capacity you never reach. Cuts of three to five hours, routinely: this is where 200 Ah, or two batteries on a 24-volt inverter, stops being an upsell and starts being the point. Cuts of six hours or more, most days: the arithmetic quietly stops working, for a reason nobody mentions in the shop.

That reason is recharging. A depleted tubular battery needs something in the order of eight to ten hours on mains to come back to full. If your area takes six hours of supply away every day, the battery never returns to where it started, and each evening begins lower than the last. Past that point you are not shopping for a bigger battery — you are shopping for a different system, which usually means solar, a larger hybrid inverter, or accepting that some hours of the evening will be dark.

Sine wave or square wave

The cheaper units produce a square or modified wave rather than the smooth sine wave the grid delivers. Fans hum on it, induction motors run hotter and less efficiently, and some electronics — certain televisions, a few chargers, most inverter air conditioners — either refuse it or complain audibly.

The price gap between the two used to justify the compromise and largely no longer does. Buy pure sine wave unless the entire load is lights and a couple of old fans and the saving genuinely matters. Anything with a motor or a circuit board in it will thank you.

Which battery, and why tubular keeps being the answer

Flat-plate batteries are the cheapest and the shortest-lived. They suit short, shallow cuts — an hour at a time, a few times a week — and they punish deep discharge badly.

Tubular batteries are the Indian default for a reason. They are built to be drained deeply and often, they tolerate heat better, and with water topped up every couple of months they last several years rather than a couple. If your cuts are long, this is the one to buy, and the taller the better within what the trolley will hold.

Lithium — specifically LiFePO4 — costs two to three times as much and is starting to make sense anyway in exactly the situation described above. It takes charge much faster, which matters when the recharge window is short; it can be drained deeper without damage; it needs no water and vents nothing; and it lasts far more cycles. The catch is that it needs an inverter whose charging profile suits it, so this is not a battery to swap in without checking, and the upfront number is real.

Whatever you buy, where it sits matters more than people expect. Batteries lose life fast in heat — a ventilated spot out of direct sun buys you months of service, and a sealed cupboard in a west-facing room takes them away.

The low-voltage trap

There is one failure mode that catches households who did everything else right. An inverter is also a charger, and it will only charge from mains that sit within its input window. On a line that sags to 170 or 180 volts through the evening — common at the far end of an overloaded lane — the inverter keeps rejecting the supply and running off the battery instead, while the household believes the power is on and the battery is filling. It is not. It is emptying, and the blackout arrives anyway.

So if your lane dims rather than dies, deal with that first, because it is a supply fault with a number attached to it in your state's regulations, not something an inverter can fix. Low voltage is a fault, not weak power sets out what the declared voltage is, where the floor sits, and what your discom owes you when it is not met.

What not to ask an inverter to do

Air conditioners, geysers, water pumps, induction hobs, microwaves and electric kettles are kilowatt loads. A home inverter system can technically start some of them and will empty the battery in minutes doing it, usually while overheating something.

If running those through a cut is genuinely the requirement, this is a different purchase — a larger hybrid inverter with a solar array behind it, or a generator — and it should be costed as one rather than approached by buying a slightly bigger inverter every few years.

If your cuts are short, buy something much smaller

For a flat where the power goes for forty minutes at a time, a whole-house inverter and a trolley battery is an expensive answer to a small problem. A mini-UPS for the router keeps the internet and the phones alive through a short cut for a fraction of the price and the space. A rechargeable fan and a couple of rechargeable lights cover the rest of it.

This is also the sensible answer for renters, who otherwise buy a system, maintain it for two years, and then find out what moving a filled tubular battery across a city costs.

Where to look

We link to category listings rather than specific models, on purpose: prices move, stock changes, and manufacturers quietly revise a model without changing its name, so a guide that names one product ages into being wrong. Match what you find against the numbers above rather than against a star rating.

• Pure sine wave home inverters

  Check the continuous watt rating on the specification, not the VA in the model name

• Tubular inverter batteries

  150 Ah for cuts of two to three hours, 200 Ah or a pair beyond that

• Mini-UPS for a Wi-Fi router

  The cheapest useful thing on this page if your cuts are short

• Voltage stabilisers

  Protection for a fridge on a sagging line — treatment for the symptom, not the fault

Questions people actually ask