I have one of these in my boat. I think it is a great charger. It automatically divides up the 20 amps total to where it needs to go. So if one of the batteries gets fully charged, the 20 amps is divided up between the remaining 2 batteries and so forth. You can also have 2 AGM batteries and 1 Flooded battery or other combinations. It can also be used for a 3 battery trolling motor system where the 3 batteries are connected in series.