How frequent and How long for?

[rickf]

To answer your question it is a good idea to start the vehicle at least once a month and let it run at a slightly raised idle for about a half hour. This will charge the batteries. As far as deep cycle batteries, they are more for RV and golf cart type use and not so much starting. they are not designed as a starting battery unless you are looking at the dual purpose deep cycle batteries.
Tell us a little about yourself, where are you from?

[raymond]

On a boat, you only use your deep cycle (read trolling motor or accessory) battery for starting the motor when your starting battery is too discharged to start the motor.

[Horst]

that is a spammer. He simply copied and pasted the text from the very first post of this thread

[rickf]

Good catch Horst, I saw his IP went back to India so I suspected as much. That was why I asked where he was from. I didn't think I was going to hear from him again.