A while back I bought a Missouri Wind and Solar circuit / charge controller and it is very simple, but very high amp capability, in fact it is really only limited by whatever you throw at it for relays or solenoid switches.
It's been doing the trick controlling 40A of current, through a relay rated at 80A.
There is only one thing I do not like about their design theory.
The default is charging; i.e. the circuit controls dump, or lack of charge. Which means, when the controller fails, the energy is free to come on in, and ruin your battery bank.
I would like to use a PICAXE or Arduino and use this same concept, but reverse that ideology; have the unit engage charging and default to no charging during failure. It'd cost, maybe 150-300 mA of current during charging.