I use the deep cycles for starting too, even though that's really not the best use for them, it's really kind of a no-no but you can do it. The deep cycle battery has less Cold Cranking Amps (CCA) than it's Marine counterpart, which is designed for starting motors and providing more amps in a burst rather than sustained amperage like a deep cycle. I usually only have to start my motor 5 times or less every time I fish and only the first start is a cold start, so I can live with that small misuse of the battery. In fact, the CCA's of these new deep cycyle gels batteries is comparable to the CCA's of the lead acid predacessors, so maybe it's not hurting them all that much. If you use 2 batteries, make sure to switch one into standby before starting with the other.

The charging cycle is different and does require a charger that can adjust the charging rate. Basically the recharge cycle is done in 3 parts, 1st part, pour in the charge as fast as the battery will take it, 2nd part, slow down the charge by about 40%, 3rd part, finish up with a trickle charge. Each battery manufacturer will have a slightly different variation and will provide the info on how best to charge. You may need a new battery charger or at least a solid state one to provide the variable charge rate.

I usually charge up the day/night before I go and when I get back I hook them right back up. Don't let them sit on less than a full charge, that will cause less life and charging capability (memory). The time to recharge has been about the same overall, maybe it can trickle a little longer but that's hard to say for sure. The bottom line is that the gels can hold more power and for downrigger fishing that's the ticket for a full day of up and downs.

My understanding is that if you take a new battery, fully charge it up and then completely drain it, it's memory is 50% of it's original capacity. If you were to repeat that again, the battery would be at 25% of it's original capacity. That's why it's so important to keep them fully charged and get them right back on the charger when you're done. You should be able to get a good 4 years out of these new batteries if you take care of them.

One last thing. One of the biggest enemies to your battery is corrosion, which is everywhere on the boat. It causes the battery to have to provide more amps (due to a voltage drop at the load)when terminals are corroded and this leads to premature failure of batteries. Keep you terminals and wiring corrosion free for maximum life. I usually re-wire my setup every 3-4 years and notice a big improvement in performance everytime I do.