I need to buy a new starting battery for my bass boat. It tests ok, but if I fully charge it on Monday, by Wednesday it's started to lose the charge, and I don't trust it to run the electronics for a full day on the water and still start the boat.

I may only run the big motor for 30 minutes during the day, so that's all the alternator time it gets, and since all the electronics are on that one battery (two fish finders (front and rear), GPS, livewell) I need the battery to be a deep cycle unit with sufficient power to crank the engine at the end of the day.

At the moment, I keep jumper cables in the boat in case I need to jump the starting battery from the trolling batteries, but that means unwiring the trolling batteries since they are wired serially to provide 24 volts for the trolling motor.

Anyone have any experience with a starting/deep cycle marine battery that they can recommend?

Check out the Optima line. They are expensive but it is an awesome battery. I have had one in my boat for two years now and not one problem.

No specific experinece with the marine stuff...but Optima has a pretty strong following...I put one of their redtop's in my truck and the guy installing it swore they were just the best.  Not cheap but good stuff. I know the auto stereo guys swear by their deep cycle yellow tops...

Why not get a separate battery to run your electronics off of, if you tie it to the primary your secondary batter will charge as well.

Get an Optima blue top, and consider adding a solar charger, or a 110V maintainer.

Quoted: Get an Optima blue top, and consider adding a solar charger, or a 110V maintainer.

+1 on the Blue Top

Or grab a CAT battery.  

Well, I'm off to the local Sears Auto Center to pick up a Blue Top (D34M) for $149.99. Any disadvantage to just wiring it in parallel with the existing battery? Or should that only be done with two identical batteries?

use a matched pair, and add a battery switch.

Swapped the new battery in. The D34M is an 870/750 CA/CCA rated battery with 120 reserve  minutes rated for starting and deep cycle.  The battery I pulled out was an AC Delco Marine Starting battery rated at 650/475 CA/CCA and not a deep cycle unit.  It's an inappropriate battery for the boat (I bought the boat used) especially given the way the boat is wired, and explains why I was having the problems I was.  I'll take the boat out tomorrow and see how the new battery does.

Thanks for the suggestions.