Will the split charge overcharge my battery?
absolutely no chance of the split charger overcharging your battery. imo they are a waste of money the ammount of charge that trickles into the battery is no good, we have to charge ours every night in order to keep it topped up.
also the main thing about leisure batteries is that they are "slow charge" "slow discharge" they are designed to discharge slowly, that is why they are great for wfp all day, but dont try to recharge them quickly with a super fast charger or you will cook the battery and it will not last very long