176 dual battery install - second opinion

Looks fine. I’d add a fuse in the + line to your solar charge controller. 20A will do, and also consider a 40A switchable circuit breaker in the main battery + line rather than a disconnect switch. The closer your over current protection is the batteries the safer you are from any shorts than might occur downstream.

Jato is right about not connecting an aging or heavily cycled battery in parallel with a new one, they will be imbalanced. If you do get two new batteries, consider getting two 6 volt golf cart deep cycle batteries in series, they will tolerate discharging better than the Dekas.

Thanks for the tip about the fuse in the + line to the solar charger. Hadn't thought about that. It came from FR without an inline fuse and I am quickly learning that they don't necessarily do things the right way all the time.

To clarify my fuse/ circuit breaker recommendations:

Your Renogy kit is likely 100 watts which has a short circuit current of 6A. Code requires you to multiply that by 1.56 to avoid nuisance trips and for enhanced output due to cloud reflection. That puts you at just below 10A. By going with 20A you could add a second solar module. The 8 awg wires themselves are good for 40A as Colt says so you could do that but it’s not necessary.n

The 8 awg positive wire to the rpod panel should be protected at 40A, that’s also what’s in the panel itself. That one can be a manual operated circuit breaker so you don’t also need a battery disconnect.

In large parallel battery banks you place a fuse in the positive output (assuming a negative ground system) of each parallel battery string, and then combine them at a separate connection point, like a dedicated bussbar or the input to the battery disconnect. I wouldn’t put a fuse in the negative jumper though because if that blows you’ve lost your ground reference. In practice no one does internal battery system fusing with a small dual battery system. You just use heavier gauge jumpers instead, and you’re already doing that. Another benefit of using 2 6V batteries in series is that the battery fuse/circuit breaker protects everything as there is only one current path.,

More like an old mechanic’s tale. The other battery type that didn’t do so well sitting on concrete was the old glass jar cells which had a tendency to break when not in a protective rack. Plastic cases solved all those problems.