My boat has this white switch with the wires off and the red one below connects the service battery.
What should this white switch do?

It gives your voltage to each battery individually when you flick it back and forth. But looks like someone has made some adjustments to your battery switch panel. There should be a gauge where that little cigarette oval emblem is.

Looks like they replaced the voltage gauge with the battery disconnect switch in the middle, so your toggle switch does nothing.

Thank you .

Thanks for the image, I'm not going to put the voltmeter so I don't lose a battery.

Looks like to me the battery switches are installed on the wrong side of the panel too?

The switches are on the back seat base and you are looking toward the stern as you look at them, so it is correct.

I was thinking that the switches needed to be mounted on the front side of the panel. Do you think those have been replaced and there was not enough room?

That's the way Cig does them them.
Instead of surface mounting them, they mount them from the back to have smooth panel so to speak.
He should have a door that swings down.