For the last 3 years I have been running Deka brand Sealed Gel batteries and love them. I will never willingly have another boat with lead acid batteries. The sealed gels will never leak, never corrode on the terminals, can be ran upside down if you wish, never have to have water added or checked. They don't leave an acid puddle in the bilge, and you don't have to worry so much about them developing memory. In my rig I have been using 2 D4 Seamates. These are the small Cat size battery. I run a 24 volt trolling motor hard, all my lights at night and even the engine off just the 2 batteries. I have fished 2 tournaments 2 weeks apart without recharging. I goofed once and cut the power off to my outlet in the garage and didn't catch it till I was pulling out that morning. No problem what so ever. Had plenty of power. These batteries also come in Group 31, 29 and 27 as well.
Gel batteries charge very fast. My D4's will charge after a day's tourney in less than 8 hours and they are the size of 2 Group 29's put together. One of the reasons you have to change the cards in the Dual Pros are the fast rate of charge. Since they charge so fast, you have to lower the voltage to slow it down so as not to blow the caps off of them. The 1 downside to a gel is it has slightly less amps than the equivalent size Lead Acid. Where a group 29 Lead acid has just over 800 MCA, a group 29 Gel probably only has about 700 MCA. Early on, there were some gels and AGM's introduced that were much much smaller in size than the normal group 29 and 31 marine batteries. People hated them because they didn't last. My suggestion with gel would be to go 1 larger size than you used with lead acid. If you use group 29 normally, then go with group 31 in gel. A gel will also discharge much more fully than a lead acid, and unlike lead acid, it gives full power till it quits. Prior to going to the gels, I used to have 3 group 29's all the time, and sometimes carried 2 extra trolling batteries in heavy wind or at night. Since I went to gels, I have never ran short of power, and maintenance for them is plugging the Dual Pro in. In my way of looking at it, batteries have been a major pain in the you know where on boats for years. Going to gel has eliminated those chores and problems for me.
You do have to do a little trick to your charger though. I use a Dual Pro onboard charger, and I had to send it to CSI in Nashville to have the cards changed over to Gel Type cards. The regular lead acid card charge too much voltage for the gels. Figure out how to stuff that onboard in there, it will save a lot of trouble.
Skipper