Hi,

We have a small solar system at the bach to run house lights and chargers etc (12V) (we have no mains connection, nor the ability to get one).

We have 210 Ah of AGM batteries (2 x 105Ah), charged by 2 x 150W solar panels though an MPPT controller. This is OK.

I have sourced a really sharp deal on two more batteries - 155Ah Wet Cell Depp Cycle batteries (x 2).

I am looking at getting another two panels, and another MPPT controller, so charging this bank of batteries is fine, it is using them that I am wondering about.

Does anyone know of a way of parallel wiring the output of both the above banks of batteries (we need 12V output) so that they aren't 'backcharging' each other (thereby confusing their respective MPPT controllers).

Failing that, is there an automatic switch that would switch from one bank to the other in the event the first bank gets below (say) 50% charge and then switches back when the first bank is recharged? I know I can get manual switches (as used on boats/caravans), but if I left it manual, it would not get switched over until the battery bank was flat, thereby reducing overall battery life.