How Long Will an Inverter Battery Really Last? (India 2026)

Name: Inverter battery backup time in India by capacity and load (2026)
Creator: PakkaPick
Published: 2026-08-14
License: https://creativecommons.org/licenses/by/4.0/

A “150Ah” battery sounds like a lot — but you never get all of it. On paper it holds 1,800 Wh; in reality you can only safely use about half of a lead-acid battery, and the inverter loses ~15% more, leaving roughly 765 Wh usable. That's about 2.5 hours on a 300W load(fans, lights and a TV), not all night. Here's the real backup by battery size and load, and why lithium changes the maths.

Last updated: 14 August 2026Sources: battery depth-of-discharge norms, inverter efficiency, appliance wattages

In short: a 150Ah/12V battery holds 1,800 Wh on paper but delivers only about 765 Wh— because lead-acid should be discharged only to ~50% and the inverter loses ~15%. That's roughly 2.5 hours on a 300W load (fans + lights + TV) or ~6.4 hours on a light 120W load. A lithium battery of the same Ah gives about 1.8× more(you use ~90%, not ~50%). To estimate your own: backup hours = (Ah × 12 × DoD × 0.85) ÷ load watts.

Key Numbers at a Glance

~765 Wh

Usable from a 150Ah lead-acid battery

of 1,800 Wh nameplate — under half

~2.5 hrs

150Ah lead-acid on a 300W load

fans + lights + TV — not all night

~1.8×

More backup from lithium (same Ah)

you use ~90% vs ~50%

~50%

Of a lead-acid battery you can safely use

deeper cycling shortens its life

Load = time

What decides backup, with battery size

halve the load, double the hours

9 / 60 / 110 W

LED / fan / TV — plan your load

from our appliance running-cost data

Use this data

The full table as a CSV — usable Wh and backup hours by battery Ah and load, lead-acid vs lithium. Free to reuse with attribution (CC BY 4.0).

How to cite: PakkaPick, “Inverter Battery Backup Time in India (2026),” pakkapick.in/inverter-battery-backup-time-india-2026 — CC BY 4.0

Download CSV

Real backup time by battery size (lead-acid)

Usable energy is only about 42% of the nameplate (50% depth-of-discharge × 85% inverter efficiency). Hours at three typical loads:

Inverter battery usable energy and backup hours by capacity and load, lead-acid.
Battery (12V)	Nameplate Wh	Usable Wh	Light (120W)	Medium (300W)	Heavy (500W)
100 Ah	1,200	510	4.3 h	1.7 h	1.0 h
135 Ah	1,620	689	5.7 h	2.3 h	1.4 h
150 Ah	1,800	765	6.4 h	2.5 h	1.5 h
200 Ah	2,400	1,020	8.5 h	3.4 h	2.0 h

Loads: Light ~120W (~3 lights + 1 fan + router); Medium ~300W (~4–5 lights + 2 fans + TV); Heavy ~500W (+ fridge / more fans). Assumes a single 12V lead-acid (tubular) battery at 50% depth-of-discharge and 85% inverter efficiency. A tired or partly-charged battery delivers less; a brand-new one a little more. One real-world catch: lead-acid Ah is rated at a slow 20-hour discharge, and at inverter discharge rates usable capacity drops a further ~15–25% (the Peukert effect), so lead-acid backup at Medium/Heavy loads runs a bit shorter than shown — lithium is largely unaffected, widening its real-world lead.

Lithium vs lead-acid — same Ah, ~1.8× the hours

A lithium (LiFePO4) battery lets you use ~90% of its capacity against ~50% for lead-acid, so the same 150Ah delivers far more usable energy:

Backup hours of a 150Ah lead-acid vs lithium inverter battery at three loads.
Load	150Ah lead-acid (~765 Wh)	150Ah lithium (~1,377 Wh)
Light — 120W (~3 lights + 1 fan + router)	6.4 h	11.5 h
Medium — 300W (~4–5 lights + 2 fans + TV)	2.5 h	4.6 h
Heavy — 500W (+ fridge / more fans)	1.5 h	2.8 h

Lithium also lasts far more cycles (~3,000–6,000 vs ~500–1,500 for lead-acid), charges faster and needs no water top-up — but costs roughly 2–3× more upfront. For heavy daily use it usually wins on cost-per-usable-unit over 8–10 years; for light or occasional backup, lead-acid is still fine.

Work out your own load

Backup hours = (Ah × 12 × depth-of-discharge × 0.85) ÷ your load in watts— DoD is ~0.5 for lead-acid, ~0.9 for lithium. Add up what you'll actually run:

Typical appliance power draw for estimating inverter load.
Appliance	Typical draw
LED bulb	~9 W
Ceiling fan	~55–75 W
Television	~110 W
Refrigerator (running)	~150 W
WiFi router	~10 W
Laptop	~50 W

Wattages match our appliance running-cost data. A fridge and other motor loads draw a brief surge when they switch on, so leave some headroom. Example: 150Ah lead-acid on 300W = (150 × 12 × 0.5 × 0.85) ÷ 300 ≈ 2.5 hours.

Frequently Asked Questions

How long will a 150Ah inverter battery last?

On paper a 150Ah 12V battery holds 1,800 watt-hours, but you only get about 765Wh out of it — because a lead-acid battery should only be discharged to ~50% to protect its life, and the inverter loses ~15% converting DC to AC. At a 300W load (say 4–5 LED lights, two fans and a TV) that is roughly 2.5 hours; on a light 120W load (a couple of lights and a fan) about 6 hours. So a 150Ah battery runs your essentials for a few hours, not all night.

Why doesn’t my inverter battery last as long as I expected?

Two reasons that stack up. First, a lead-acid (tubular) battery should only be discharged to about 50% of its capacity — going deeper repeatedly shortens its life sharply — so half the nameplate is effectively off-limits. Second, the inverter itself wastes about 10–15% turning the battery’s DC into mains AC. Put together, a 150Ah / 12V battery with 1,800Wh on the label delivers only around 765Wh of real, usable energy — about 42% of what the number suggests. That gap, not a faulty battery, is why backup feels short.

Lithium vs lead-acid inverter battery — which lasts longer on backup?

A lithium (LiFePO4) battery gives roughly 1.8× the backup of a lead-acid battery of the same Ah, because you can safely use about 90% of it versus about 50% for lead-acid. So a 150Ah lithium delivers ~1,377Wh usable against ~765Wh for a 150Ah lead-acid — nearly double the hours. Lithium also lasts far more charge cycles (typically 3,000–6,000 vs 500–1,500), charges faster, and needs no water top-up — but it costs roughly 2–3× more upfront. Over a 8–10 year horizon lithium often works out cheaper per usable unit; for a small or rarely-used backup, lead-acid is still fine.

How do I calculate my inverter’s backup time?

Use: backup hours = (battery Ah × 12 × depth-of-discharge × 0.85) ÷ your load in watts. Depth-of-discharge is about 0.5 for lead-acid and 0.9 for lithium, and 0.85 is the inverter’s efficiency. Add up the watts of what you’ll run: an LED bulb is ~9W, a ceiling fan ~55–75W, a TV ~110W, a fridge ~150W, a WiFi router ~10W. For example, a 150Ah lead-acid battery on a 300W load = (150 × 12 × 0.5 × 0.85) ÷ 300 ≈ 2.5 hours.

Does a bigger battery (more Ah) give proportionally more backup?

Yes — backup time scales almost linearly with capacity, so a 200Ah battery gives about a third more than a 150Ah, and two 150Ah batteries on a 24V inverter roughly double it. But bigger batteries cost more, weigh more and take longer to recharge — and if your area has long or frequent cuts, a big battery may not fully recharge between outages, so it never delivers its full rated backup. Sizing the battery to your real load and outage pattern matters more than just buying the biggest one.

Sources & Methodology

Backup hours = battery Ah × 12V × depth-of-discharge × 0.85 inverter efficiency ÷ load in watts. Usable energy = nameplate (Ah × 12V) × DoD × efficiency. Figures are for a single 12V battery; 24V/48V systems (two or four batteries) scale the energy up proportionally.

Depth-of-discharge — lead-acid / tubular batteries are rated for long life at ~50% DoD; LiFePO4 (lithium) at ~80–90%. Discharging lead-acid deeper repeatedly cuts its cycle life sharply.
Inverter efficiency — a home inverter loses ~10–15% converting battery DC to mains AC; ~85% is a typical round figure.
Appliance wattages — LED ~9W, ceiling fan ~55–75W, TV ~110W, fridge ~150W (running); consistent with our appliance running-cost data.
Battery life & cycles — typical cycle life ~500–1,500 for lead-acid vs ~3,000–6,000 for LiFePO4 (manufacturer datasheets).
Discharge rate (Peukert effect) — lead-acid Ah is rated at a slow 20-hour discharge; at inverter loads real usable capacity falls ~15–25%, so lead-acid backup at higher loads runs shorter than these ideal figures. LiFePO4 is largely unaffected.

Figures are estimates for guidance: real backup depends on the battery's age and charge level, the exact load, temperature and inverter model. This page contains no product prices.

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