Originally Posted by SimonV
From what I have read, one of the big positives for going from wet to AGM is you do not need to change your charging systems. When I bought my boat it came with Gels and I could not be happier, when i need to replace them it will be with the same.
You can often use flooded voltage settings but the acceptance rates of the batteries can tend to smoke small or factory alts not built to handle or disperse the heat. At a minimum I recommend an alternator temp sensor... I have two alternators on my bench right now both cooked by AGM banks.
With a single battery you can often do fine and some factory alts have built in temp compensation but you'll charge very sloooowly when they heat up. However when you get into bank of AGM this is where you really should complete the rest of the system.
These are expensive batteries that benefit from temp compensated charging and temp limited alternators will also benefit.
This is not just limited to AGM's and even a flooded bank that is much bigger than the alternator can suffer the same fate.