How long it lasts
How long will a 150Ah battery last?
On a single 12 V tubular battery, a 150Ah battery runs a 300 W load, about three fans, four LED bulbs and a TV, for roughly 3.5 to 4.3 hours. Halve the load and the backup roughly doubles.
| Battery (12 V, tubular) | 200 W load | 300 W load | 500 W load |
|---|---|---|---|
| 100Ah | 3 h 34 min to 4 h 20 min | 2 h 23 min to 2 h 53 min | 1 h 26 min to 1 h 44 min |
| 150Ah | 5 h 21 min to 6 h 30 min | 3 h 34 min to 4 h 20 min | 2 h 9 min to 2 h 36 min |
| 200Ah | 7 h 8 min to 8 h 40 min | 4 h 46 min to 5 h 47 min | 2 h 51 min to 3 h 28 min |
The backup formula, and why ads show more
Brand guides often use Ah × volts × 95% ÷ load. That assumes the battery empties completely and the inverter loses almost nothing. In practice the inverter cuts off before a lead-acid battery is flat, heavy loads drain it faster than its rating, and home inverters convert about 85% of the energy. We use 70 to 85% usable for tubular batteries and 90 to 95% for lithium (LFP), which is why our figure is lower than the box.
Which inverter size do you need?
Inverters are rated in VA. Divide your load in watts by 0.8 and pick the next size up. Above about 1,100 VA most home inverters need two batteries in series (24 V).
| Your load | Inverter | Batteries |
|---|---|---|
| Up to 480 W | 600 VA | 1 × 12 V |
| Up to 720 W | 900 VA | 1 × 12 V |
| Up to 880 W | 1,100 VA | 1 × 12 V |
| Up to 1,200 W | 1,500 VA | 2 × 12 V (24 V) |
| Up to 2,000 W | 2,500 VA | 2 × 12 V (24 V) |
Tubular or lithium?
Tubular lead-acid batteries cost less upfront and suit a few power cuts a week. They need water top-ups and last roughly four to six years. Lithium (LFP) batteries cost more but give more usable backup from the same Ah, need no water, charge faster and last longer. If you have daily cuts of several hours or plan to add solar, lithium usually works out cheaper per year. Check that your inverter supports lithium before you switch.
Frequently asked questions
How many hours will a 150Ah battery run?
About 3.5 to 4.3 hours at 300 W, 5.3 to 6.5 hours at 200 W, and 2.1 to 2.6 hours at 500 W on a 12 V tubular battery.
How long does a 200Ah battery last?
About 4.8 to 5.8 hours at 300 W, or 7.1 to 8.7 hours at 200 W on a single 12 V tubular battery.
How many batteries does a 1,500 VA inverter need?
Usually two 12 V batteries in series (24 V). 600 to 1,100 VA inverters usually run on one.
How do I get more backup?
Cut the load first: LED bulbs and BLDC fans can halve it. Then add capacity: a bigger Ah battery, a second battery, or lithium.
Can a home inverter run an AC?
A 1 ton inverter AC needs about 1,000 W and more at start-up, so it needs a large inverter and battery bank. On a normal 150Ah battery it would last well under an hour.
Not sure what your load is? Add it up with the home load calculator. Our assumptions are on how we calculate.