Redarc, make a device which I believe is called a charge equaliser, to over come this issue, but don't hold me to it.
Also their bc-dc chargers can have a 24 volt input and output a 12volt charge.
I'm going to run 24volt start and charge then run into one of the redarc products, possibly their BMS system to charge whatever 12 volt deep cycle batteries I decide to use for all other functions.
Only down side is I may end up with 4 batteries and expensive.
On the up side, gives me many options if I'm away and I should have a problem, these systems are also good for solar input as and I seem to recall the BMS can deal with 240volt input as well.
Great reliability.
Anyway, that's my penny's worth.
I'd leave yours as 24volt, get a charge equaliser and continue onwards.
I have some 24 to 12 volt converters if you decide to go that way, give me a yell.

