Replacing Batteries on a 420

[1000islander]

I will be changing the batteries(type 31) on my 420 SUndancer this spring. I was considering AGM batteries. My question is do I have to be concerned about the current battery charger I have and will it work with the AGMs? Also, what brand should I consider. The boat has 480 CE Cummins, Bow and Stern Thursters, and Onan Generator.

Thanks for your input......