[Closed] charging batteries and split charge relay question

ive got 2x 115Ah batteries in the van and a Durite VSR so they charge when the engine is running.

Ive just realised the VSR works both ways so if i have an electrical hook up then its charging the 2x 115Ah lesiure batteries but also the van starter battery which is only 70Ah.

So, if im running a fridge and the charger is supplying more than a trickle charge to keep the leisure battieres topped up, is this going to overcharge the van starter battery as its a lower capacity, or is it not an issue?

I could fit a switch into the VSR ground wire so i can stop it activating when on hook up if it is an issue.