Ok, hi forum!

I am in the process of converting my transit van into a camper.

I have a comprehensive wiring diagram which satisfies my requirements. I bought two hella relays for the wiring. One relay is for charging (typical aditional battery charging),  and the other one is for isolation (to keep fridge running when van is driving). The trouble is, i think the isolation relay on the diagram is a little different to the charge relay. Are there different types of relays or are they all generic, automated switches?

Any info or pointers would be appreciated. (the diagram is from haynes build your own motorcaravan if it helps)

Cheers!

Pete