Off-Grid Runtime Calculator
How long will your backup power last?
Off-Grid Runtime Calculator
How long will your backup power last?
Formula
Runtime = Usable Wh / Total WattsHow to Use
- 1Enter battery capacity — Input your total battery bank capacity in Ah or kWh.
- 2Enter total load — Sum the wattage of all devices running on your batteries.
- 3Set depth of discharge — Choose your max DoD (50% for lead-acid, 80% for lithium).
- 4Get runtime — See how many hours your system will last at the given load.
Frequently Asked Questions
How long will a 100Ah battery last?
A 12V 100Ah battery has 1,200Wh. At 200W load with 50% DoD: about 3 hours. With 80% DoD (lithium): about 4.8 hours.
Does temperature affect battery runtime?
Yes. Cold temperatures reduce lead-acid capacity by 10-20%. Lithium batteries perform better in cold but should not be charged below freezing.
Should I include inverter losses?
Yes. Inverters are 85-95% efficient. Add ~10% to your AC load to account for conversion losses from DC batteries.
How do I extend my runtime?
Reduce load (turn off non-essentials), add more battery capacity, or supplement with a generator or solar panels during the day.