I built a solar powered backup battery a couple years ago, but decided to make a better solar battery bank. I originally thought I needed more room for more 12v lead acid batteries when I built the last version. I never added 12v lead acid batteries, because LiPo batteries started looking appealing, and did not want to waste time or money on increasing amps, with more lead acid batteries. They are also quite heavy.
The lead acid batteries I have, still have plenty of life, so I decided to re-use them. The new version is more compact, and better insulated against weather.
I re-used 4 12v 7AH and 1 12v 8AH battery. I secured them into an internal holder, made of plywood. The internal holder protects the batteries, prevents movement, makes the carrier more rigid, and gives me a place to mount my screw block terminal for a cleaner wiring job.
The battery box is tactical ammo box, from Harbor Freight. On its own, its somewhat flimsy and unimpressive, but the dimension were perfect for 5 12v lead acid batteries. Its also waterproof, and has a nice little ‘top compartment’ for protecting toggle switches from the elements. The wiring is nice and clean, and fairly straight forward. All wires go to their respective polarity on a terminal block.
Three switches run three different plugs. Two of those switches run waterproof cigarette lighter sockets, which is how I am attaching the solar cell during the day time. A third switch runs a dual 5V 2.1A usb port, although this one, with a voltage indicator built in, would be the better option if I didn’t already have a mini digital voltmeter.
This reduces the need to start the car and burn fuel, and lets us keep phones, GPS, watches, bluetooth speakers, and headlamps fully charged.