Newer heart inverters
do not have dip switches. The appropriate charging protocol is selected via push buttons on the front of the unit. If you had the heart set for flooded batteries, it will trash the gel cells.
Another source of damage is the regulator on the engine alternator. If it is the stock alternator that most engines come with, it will probable be internally regulated and set for flooded batteries. If you left for a cruise after the batteries were fully charged at the dock, the alternator would immediately start pusing the voltage up to try to cram more amps into the batteries.
Gel battereis should not be charged using an internally regulated alternator unless you know there is some way to adjust the regulator for lower voltages.
I have used flooded batteries, gel cells and am now giving AGMs a try. All have their advantages and drawbacks. The negative on flooded cells is their need for maintenance. On my last boat I had to use a mirror and flashlight to see if they needed water...That was a big "pita" . Flooded cells bring with them the risk of injury by the corrosive electrolite. The can also be trashed by being completely drained. They are cheap and it is possible to monitor their condition with a hydrometer. They also (as someone pointed out, give you the most amp hours per buck) Now that sealed alternatives are available I wont use flooded batteries.
Gel Cells are sensitive to charging voltage but have more capacity than AGMs. There is still debate of which of the sealed options provide more cycles in their lifetimes. BTW, cycles is not the name of the game, total amp hours in the battery''s life is the thing to worry about for economic reasons.
AGMs have the advantage that they can be installed in any position and dont loose capacity as a result. Gels can be installed on their side but loose about 10% of their capacity. AGMs have very high exceptance rates. This is a double edged sword. You can charge faster but need to watch temp and have some way to reduce alternator output (especially in hot weather). AGMs can be treated like flooded batteries in terms of the voltages they will tolerate. They have slightly lower capacity than flooded cells.
I just put 5 4d agms on my new boat. The are charged through the heart inverter
/charger and using a balmar high output alternator and max charge regulator. I installed the temp monitoring option from the heart. It senses battery temp and warns of problems. The balmar max charge has two temp sensors. One is on the alternator (to prevent it from overheating when charging greatly discharged batteries, and one to the batteries themselves. If the max charge senses elevated battery temp it halves the output of the alternator.
If you have indeed trashed some of your gel cells maybe you can get by on the remaining cells for a while. Dont put new gels in a bank with old ones. The old gels will quickly drag your new batteries down to their state of health.
If you have a stock alternator and dont want the expense or hassle of changing it out, use flooded batteries or AGMs which can handle the output of the alternator. Make sure your heart is set for the type of battery you have chosen. If the heart is set for gels it will consistiently undercharge your flooded batteries.