The tubular lead-acid battery under the stairs has been the standard answer to Indian power cuts for thirty years. It works, it is cheap to buy, and almost every electrician in the country can install one.
It is also 60 kg of maintenance that needs a ventilated corner, wants distilled water every six weeks, and will need replacing three or four times over the life of the inverter sitting on top of it. Lithium changes all of that, and unlike the vehicle case, the argument here is not primarily about money.
Backup is a different duty from traction
This matters because it changes which battery properties are worth paying for.
A vehicle battery is deep-cycled every day, drawn at high current, and lives in whatever temperature the road provides. A home backup battery spends most of its life fully charged and doing nothing, discharges occasionally and gently, and sits in a corner at roughly room temperature.
| Vehicle traction | Home backup | |
|---|---|---|
| Cycles per year | 300–600 | 50–300, depending on supply reliability |
| Typical discharge rate | 0.3–0.6C | 0.1–0.3C |
| Time spent at full charge | Minimal | Most of its life |
| Temperature | Ambient extremes | Indoor, more stable |
| What limits life | Cycle ageing | Calendar ageing |
That last row is the important one. A backup battery in a reliable-supply area is not worn out by use — it is worn out by time, sitting at full charge. Which means the specifications that matter are calendar life and float tolerance, not cycle count. It also means the manufacturer’s cycle rating, which is what most marketing leads with, is largely beside the point for this application.
The comparison that actually matters
Take a household that wants around 2 kWh of usable backup — enough for lights, fans, a television and a router through a four-hour cut.
| Tubular lead-acid | LFP lithium | |
|---|---|---|
| Usable depth of discharge | 50% | 90% |
| Nameplate capacity needed | ~4.0 kWh | ~2.2 kWh |
| Physical form | 2 × 150Ah tubular | One 48V 45Ah pack |
| Weight | ~120 kg | ~22 kg |
| Floor space | Trolley, ventilated | Wall-mountable |
| Maintenance | Water every 4–6 weeks | None |
| Service life | 3–5 years | 8–12 years |
| Charge time from empty | 8–10 hours | 2–3 hours |
| Efficiency | ~75% | ~95% |
Five things in that table are worth drawing out.
Weight and space. 120 kg on a trolley in a ventilated corner becomes 22 kg on a wall. In a flat, that is often the whole argument.
Charge time. This matters far more than people expect in areas with frequent cuts. A lead-acid bank that takes nine hours to recover has not finished recharging before the next cut arrives, so it is permanently at partial charge — which is also the condition that shortens its life fastest. Lithium recovers in two to three hours and is ready again.
Maintenance. Watering a tubular battery is a small job that is easy to skip, and skipping it in an Indian summer will halve the battery’s life. Removing the possibility is worth something.
Ventilation. Lead-acid gasses hydrogen while charging and needs airflow. Lithium does not, which is why it can go in a cupboard or on a wall where lead-acid cannot.
Efficiency. A quarter of what you put into a lead-acid bank is lost as heat and gassing. With lithium it is about 5%. Over years of daily cycling, that adds up.
The cost, honestly
Lithium costs roughly two to three times more up front for the same usable energy. Over a ten-year horizon:
- Lead-acid: two 150 Ah tubular batteries at around ₹18,000 a pair, replaced every four years — three sets in ten years, roughly ₹54,000, plus water and the labour of changing them.
- Lithium: one pack, still working at year ten, at perhaps ₹45,000–55,000.
Over a decade the two land in much the same place, with lithium slightly ahead once charging losses are counted. That is a weaker financial case than the e-rickshaw comparison, where lithium wins outright, and it would be dishonest to present it otherwise.
The money is close to a wash. What is not close is 22 kg on a wall instead of 120 kg in a corner, no watering, no hydrogen, no ventilated space, recharging in two hours instead of nine, and not doing any of this again for a decade. Home backup buyers are usually buying the absence of hassle, and the arithmetic merely has to not be an obstacle.
Sizing it
Two numbers, and people routinely get the second one wrong.
The inverter: sized on surge
Every appliance has a running wattage and a starting wattage. Anything with a motor or a compressor — fridge, pump, mixer — surges to two to six times its running figure for a second or two.
The inverter must survive the largest single surge occurring while the ordinary load is already running. A 0.5 HP pump runs at 375 W and surges to around 1,900 W; starting it while 600 W of lights and fans are already on is a momentary 2,500 W demand.
Remember also that inverters are rated in VA, not watts. At a domestic power factor of about 0.8, a 1,500 VA inverter delivers roughly 1,200 W continuously. Treating VA as watts is the single most common sizing error there is.
The battery: sized on energy
List what you want to run and for how long:
| Load | Watts | Hours | Wh |
|---|---|---|---|
| LED lights × 6 | 60 | 4 | 240 |
| Ceiling fans × 3 | 225 | 4 | 900 |
| Television | 100 | 2 | 200 |
| Router and chargers | 40 | 4 | 160 |
| Refrigerator | 150 | 1.5 (compressor duty) | 225 |
| Total | 1,725 Wh |
Then divide by depth of discharge and inverter efficiency: 1,725 ÷ 0.9 ÷ 0.9 = 2,130 Wh. So a 2.2 kWh lithium pack, or a 4 kWh lead-acid bank for the same result.
Why the waveform matters
A cheap inverter produces a modified square wave — a stepped approximation of mains AC. It runs a filament bulb or a heater perfectly well and is unkind to everything else.
Induction motors in fans, pumps and fridge compressors run hotter and less efficiently on it, and often hum audibly. Switch-mode supplies in televisions, laptops and LED drivers run hotter too. The damage shows up as shortened appliance life rather than inverter failure, which makes it easy to miss and easy to blame on something else.
Our Samrat Lithium Inverter produces a pure sine wave and integrates the battery, so there is no separate bank to site, wire or ventilate. For a home or shop replacing an ageing inverter and tubular set, it is a single unit rather than a project.
Samrat Lithium Inverter
Pure sine wave output, integrated lithium battery, smart LCD display and fast charging — silent, wall-mounted backup with nothing to maintain.
₹31,860 incl. GST · 24-month warranty
Shops and small businesses: a different calculation
For a household, a power cut is an inconvenience. For a shop it is closed doors, and that changes the sizing exercise entirely.
The first difference is that the loads are not negotiable. A home can sit through a cut with fans and lights. A shop needs its billing system, its card machine, its lights over the display, and in many trades its refrigeration — and losing any one of them means turning customers away.
| Load | Watts | Why it cannot be dropped |
|---|---|---|
| Billing computer and printer | 150–250 | No billing, no sales |
| Card machine and router | 40 | Card payments fail without connectivity |
| Display and task lighting | 200–400 | Customers do not shop in the dark |
| Ceiling fans | 150–300 | Customers leave |
| Refrigeration (if applicable) | 200–400 running, 1,200+ surge | Stock loss |
| CCTV | 30–60 | Insurance and security conditions |
The second difference is cycle frequency. A shop in an area with daily cuts is cycling its battery every day, which moves the duty away from calendar-limited and toward cycle-limited — and that is where lithium’s advantage widens sharply. A tubular bank cycled daily will not see four years; it will see two. On that pattern, the ten-year cost comparison stops being a wash and starts favouring lithium clearly.
The third is recharge time, and for a shop it is decisive. Two cuts in a day is common in many areas. A lead-acid bank that needs nine hours to recover simply will not be ready for the second one, so the shop is running on a partially charged battery precisely when it needs it most — and permanent partial charge is also what kills a tubular battery fastest. A lithium pack recovering in two to three hours is ready again.
The practical recommendation for retail: size the inverter on refrigeration surge if you have any, size the battery for the longest cut you actually experience rather than the average, and treat recharge time as a specification rather than a detail.
Getting the most out of it
Backup batteries are limited by calendar ageing, so the habits that matter are different from a vehicle’s.
- Keep it cool. The dominant variable by a wide margin — calendar ageing roughly doubles for every 10 °C above about 30. A pack in a sealed cupboard against a west-facing wall ages far faster than the same pack somewhere shaded and ventilated. This is the one decision that most affects how long it lasts.
- Do not worry about shallow cycling. Unlike lead-acid, LFP has no memory effect and does not need periodic deep discharges. Frequent short cuts are not harming it.
- Let it charge fully. Cell balancing only happens at the top of a charge. In practice a backup pack reaches full most days anyway, but if yours is in an area of very frequent cuts and rarely gets there, that is worth knowing about.
- Leave it part-charged if you are away. Going away for months? Around 50–60% is much gentler than sitting at 100%.
Our guide to charging habits and battery lifespan covers the reasoning in full.
Adding solar later
Many households buy backup first and solar afterwards, and that sequence works — provided the inverter can accept it.
A hybrid solar PCU combines the solar charge controller, battery charger and inverter, and manages priority between solar, battery and mains. Configured well, it runs the load from solar first, charges the battery with the surplus, draws from the battery when solar is insufficient, and touches the mains only as a last resort. That ordering is what reduces the bill; a system that charges from mains whenever it dips is quietly spending money.
If solar is a possibility within a few years, buying a hybrid unit now is cheaper than replacing a backup-only inverter later. Our Solar Inverter · DSP Sine Wave is built for this, and the solar sizing guide works through the load calculation and panel count.
What to check before you buy
Four questions, and they will tell you most of what you need to know about any lithium inverter on the market.
- Is the output a true sine wave? “Modified sine wave” and “quasi sine wave” both mean stepped square wave. Ask plainly.
- What is the surge rating, and for how long? A continuous rating alone tells you nothing about whether it will start your fridge.
- What chemistry and what cycle rating? LFP, and a cycle figure with a capacity threshold attached to it — “3,000 cycles to 80%” means something; “3,000 cycles” does not.
- Who honours the warranty, and for how long? An integrated unit is one product; make sure one company stands behind all of it.
In short
For home and shop backup the financial case for lithium is close rather than decisive — roughly a wash over ten years. What is decisive is everything else: a quarter of the weight, no watering, no ventilated corner, no hydrogen, recharging in two hours instead of nine, and one purchase instead of three.
Size the inverter on surge rather than running load, size the battery on the energy you actually need, insist on a pure sine wave output, and put the pack somewhere cool. Get those four right and it will still be working when the tubular bank you did not buy would have been on its third replacement.