two batteries

Does anyone run a second battery as an auxilary? I want a second gel cell that will have a constant charge while engine runs. But no load taken off it unless I transfer switch it. I think I need a isolator, anyone have a set up like this?

We do on a fire engine, but I'm not quite sure how it is ran....I will look and see.

We do on a fire engine, but I'm not quite sure how it is ran....I will look and see.


Yea I have seen the way it's done on police cars and other rescue aparatus, I am wondering if it's ok to do the same hook up with these computer sensitive stock trucks.

Mine is set to automatically switch over when the main battery gets too low. Not sure what would be the "correct" way to set it up to manually switch it over.