How long will my battery backup power my equipment?

To figure out how long a battery backup system will keep your equipment powered there is a fairly simple calculation you can do: ((Battery Capacity (Ah) x Battery Voltage (12V)) x Percent Discharge (50%)) / Your Equipment Load (W). So let’s say your 12V battery capacity is 100Ah and your equipment load is 50W. We use 50% discharge because you really don’t want to discharge batteries much more than 50% if you want them to have a long life. 100Ah x 12V = 1200Wh – 1200Wh * 0.5 (50% discharge) = 600Wh (adjusted battery capacity) 600Wh / 50W = 12hrs backup time. As you can see, with 100Ah of battery and 50W load, your backup time is at least 12 hours.