Transit MK7 wrote: Another question too is where is the system for splitting the 2 batteries when the ING is off? As I don’t want to remove this without knowing if my van still has the original split charge system in place. Hope that makes sense.
The original system is not a split charge as such, it's a system whereby the batteries are separated when the engine isn't running, so that the starter battery is isolated and immune to being flattened by the vehicle electrics.
When the engine is running, both batteries are being charged simultaneously.
The relay that facilitates this feature is in the battery fuse box, which is behind the batteries under the drivers seat. You should be able to hear this relay "thunk" when you turn on the ignition, and if you don't start the engine, it will disconnect (with a thunk!) about a minute or so, later.