Sorry everyone,
I have been away, thanks for all the replies.
to answer a few q's
-Same brand/model/age
-bank de-equalization happens maybe 2-3 times a year, just I forget it and have a blackout for a night 
-Battery are maintenance free deep cycle
-Charging source is approx 1500Watts of solar. (50-60Amps)
-I dont equalize as it over voltage my inverter... I might consider this for solo battery health as each cell gets an equalization.. might meaning disable inverter for a day when this happens.. not really doing this tho.
I have an image of how my batteries are wired together for 24v
replacing the batteries is an option, but Id rather not! as it's time consuming and expensive.
I am sure a simple charge balancer will help prolong the life of the batteries also.
MY ARDUINO PROJECT PHOTO,
so the plan is layed out in block form.
My main concern is how to power the arduino. I would like to via the batteries.
but external power source is possible and fine..
Most important would be getting arduino to read two analog inputs as voltage and might mean using the Grey rail as ground and Neg/Pos of the 24v for each 12v.. esentially making one of the analog inputs a -12V (Negative)
apart from that, I will use a relay board to turn on a relay with a light or other load / or additional charge from a solar panel and the arduino will decide which battery needs it.
Thinks I am unsure of, can arduino analog in take a Negative voltage?
the code would be an if statement, such as if analog 1 is higher when analog 2, then turn relay 2 on. else turn relay 1 on.
something like that.
but I dont know the important stuff like, do I need to calculate the incoming analog? what resistor would I need to use if arduino cannot read 12v.. I think it reads upto 5v? meaning I need to drop voltage with a resistor.
thanks everyone for interest in helping me.
cheers
