How to calculate how long a car battery will last as backup

[Chin_Lee]

Originally Posted by r_wellwood

5 amps, seems like a lot of equipment could run on that. Wouldn't the idea behind the backup be to maintain temperature, water flow (PH or two, return pump from sump if heater is there), and areation? Maybe some minor lighting could be powered, but why bother with keeping MH, VHO, all PowerHeads, etc going?

Strange things happen randomly in nature, and a power outage for a Fish/Reef tank for even a day should be tolerable for the system (with temperature, basic flow, and aereation maintained).

I could see something heavy-duty being necessary on a larger/complex system if say a chiller was also involved (closed loop pump and compressor).

Exactly. I think our objective is to keep our livestock alive in the event of a blackout as oppose to letting them continue thriving. So to keep them alive, give circulation and warmth. I would keep one 6060 tunze which is 13 watts and a 300w heater just to keep the display tank water circulating and heated. I will probably set the heater a ~75 which is just a little below my norm.

So if its 6600 total watts, how long will that 6600 watts last? If I wanted to know how long my 13w tunze will stay on, what formula do I use to calculate time into that equation? (sorry i'm asking you all to do my math and research )