Here's what I think.. If you are truly using this as a backup system, and are not loading the batteries except for emergencies, reduce the float voltage on the BZ to 13.8 or 13.6 and call it good. This will reduce water consumption, and maybe reduce plate degradation as well. Sulfation shouldn't be an issue as the batteries are not in regular discharge use. BZ has no software in the MPPT500 that can be changed, trust me.

If you have regular, daily loads on the system, try and get a three stage MPPT controller. Morningstar makes one as well as Outback. With only 360W of panels though, maybe a little power loss in the cabling is worth the tradeoff in a $90 charge controller. It would depend a lot on your daily electrical requirements from the system.

Let me tell you, I ran my whole, four person household on a system that was only slightly twice as big as yours, with very little generator backup, for over a year. No electric fridge or freezer then but I think that system you built is very viable for long term emergency use or even daily single room or single use loads.

Congratulations in making your system scalable. I believe you have chosen some of the basic building blocks there that can take a whole family off the electric grid if you choose (or need) to do so. I see true deep cycle batteries, high quality cabling, a good SW inverter with charger built in, DC breakers everywhere they should be... etc.

Not trying to inflate your ego but I think this is a pretty nice, easilly scalable micro PV system.. Good work.

Volvo Farmer