2nd Battery

[The Bottom Line]

Ok guys here it goes. I've been trying to read up on it but cant find the answers I'm looking for.
I own a 1989 V20 with one battery located under the removable bait bucket located next to the engine. I have all of my electronics hooked up to it and plan on adding a few lights to my boat this year. I want to add a second battery and was just wondering where everyone has placed it. There is no room for a 2nd one where my battery is now. I was thinking about putting a second one in the cabin and connecting all of my electronic to that battery.
I have a 2nd deep cycle battery in my garage.
Would I be able to use that?
And do I need to put some kind of recharging system or alternator somewhere?
Any help is greatly appreciated!
Thank you in advance.
- Jim