A few years ago I built a Monster UPS using an RV Inverter/Charger and two golf cart batteries.   Seeing as how I have a lot of extra golf cart batteries just hanging around, I upgraded it to use eight GC2 batteries (that’s 720 AH x 12 volts, or 8.6 kWh when new). Because more is better, right? (Except for the 500 lb system weight…which is probably getting close to the capacity of the steel cart I’m using to make it semi-mobile.)

The 8 GC2 golf cart batteries and large 2/0 cables with the red and black hoods over the lugs were left over after I upgraded my truck from Lead Acid batteries. The 2/0 cables are just a tiny bit larger than I need for this application…but…already had them.

The 8 six volt batteries are arranged in 4 parallel groups of 2, where each group is in series (using the short 2/0 cables) to make the 12 volt system. The yellow and black AWG 2 cables were salvaged from the wrecked Nissan Leaf I got the new LiIon batteries from. It may not look like it, but I can still get all of the battery vent cover caps off to water them (although I have to push on some of the cables here and there to do it…)

Of course, because I’d used the golf cart batteries in my truck for several years already, they don’t have their full capacity left. I used a space heater to run the pack down until the inverter automatically shut off, and got 3.74 kWh out of the system (over the course of 3.5 hours), which indicates that the batteries have about half of their original capacity currently.