How long a 100, 150 or 200 Ah inverter battery runs your fans, lights and TV
Runs in your browser. Nothing you type is sent anywhere. Updated on 24 Oct 2026.Backup time is the energy the battery can safely give up divided by the load. A 12 V 150 Ah lead-acid battery stores 1,800 Wh; using half of it and losing about 15% in the inverter leaves 765 Wh, which runs a 300 W load for about 2 hours 33 minutes. Enter your battery rating, the number of batteries and your load in watts.
| Load | 100 Ah | 150 Ah | 200 Ah |
|---|---|---|---|
| 100 W | 5 h 6 min | 7 h 39 min | 10 h 12 min |
| 200 W | 2 h 33 min | 3 h 50 min | 5 h 6 min |
| 300 W | 1 h 42 min | 2 h 33 min | 3 h 24 min |
| 500 W | 1 h 1 min | 1 h 32 min | 2 h 2 min |
| 800 W | 0 h 38 min | 0 h 57 min | 1 h 17 min |
The page opens on Backup time; pick the Battery type.
Enter the Capacity of one battery in Ah, its voltage and the number of batteries.
Enter the Load on the inverter: the watts of everything that will run together.
Read Runs for about and the energy safe to use, and open The working for each step.
This calculator answers two questions about a home inverter. How long will my batteries run this load? And what battery size do I need for a set number of hours? It uses the energy stored in the batteries and nothing else, so every step can be checked by hand.
The formula. Each battery stores its Ah rating times its voltage in watt-hours: a 12 V 150 Ah battery holds 1,800 Wh. Only part of that should be used. Lead-acid batteries, tubular or flat plate, last much longer when drained to about half, so the default depth of discharge is 50%. Lithium (LiFePO4) batteries tolerate deeper use, so the lithium default is 80%. The inverter then loses some energy as heat; 85% efficiency is typical for a home sine-wave inverter. Divide what is left by the load in watts to get the hours.
The calculator does not model the Peukert effect (lead-acid batteries deliver fewer Ah at high current than their rating), battery age, heat, or the inverter's own standby draw. Real backup is usually a little shorter than the figure shown, especially above 500 W on one battery.
The rest of the article, and all 6 questions about Inverter Battery Backup Calculator, are on the Inverter Battery Backup Calculator page.
About 2 hours 33 minutes for a 12 V lead-acid battery. The battery stores 1,800 Wh; using half of it gives 900 Wh, and an 85% efficient inverter delivers 765 Wh. Dividing 765 by 300 W gives 2.55 hours. A lithium battery of the same rating, used to 80%, lasts about 4 hours.
Depth of discharge is the share of a battery's stored energy you actually use before recharging. Lead-acid batteries wear out quickly if drained fully, so about 50% is a common limit for a long life. Lithium iron phosphate batteries handle 80% or more. A deeper discharge gives more backup today and fewer years of battery life.
No. Two 12 V 150 Ah batteries store 3,600 Wh either way: in series they make 24 V at 150 Ah, in parallel 12 V at 300 Ah. The inverter's design decides the wiring. Enter one battery's rating and the number of batteries, and the energy comes out the same.
Lead-acid batteries deliver fewer amp-hours at high current than their rated figure, known as the Peukert effect. Older batteries hold less, cold weather reduces capacity, and the inverter draws some power even with no load. The calculator leaves these out, so allow a margin, particularly for loads above 500 W on a single battery.
Formula only: no rates or limits are read from an official source.
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