VSR and battery isolator switch

[The Mad Cat]

About to wire in a VSR in a boat that has the normal battery isolator switch, battery 1, battery 2, or both. By leaving the switch on battery 1 which is the start battery the VSR will do it's thing by charging the house battery when the start battery is topped up.The VSR is the type that will let charge back to the start if the house is charged and the start are down on charge.
What will happen if someone switches the isolator to battery 2 or both?
Can any damage be done to the VSR?

Hope I have explained this properly.
Appreciate any help.

TMC

[Lovey80]

Charge should go uniformly to both batteries at the same time if they are at the same level. If one battery is lower than the other it will draw more charge. You run the risk though of flattening your start battery as well as the house battery if you leave them like that. The VSR should be fine either way.

[juggernaut]

If it is a dual sense VSR (which you indicate it is) switching the battery switch to 1 or 2 won't matter as the VSR will operate in either position.

Switching the battery switch to both will effectively override the VSR as you have electrically combined the batteries regardless of the voltage in either battery via the switch. This could result in a dud battery also flattening the remaining good battery with seconds at the most. So it is generally not recommended - unless both batteries are in good health voltage wise.

In contrast the VSR will only combine the batteries where preset minimum voltages are present in the batteries - saving you from buggering up your good battery.

In my experience switching to both doesn't bugger up the VSR.