I went to Batteries Plus today cause my bass boat battery that is less than a year old won't charge. They were checking it out and was asking me questions about it. I told them that I was using a Schumaker charger, a really good one and it just says check battery. I charged my other two boat batteries and they did fine. While they were still messing around, I was reading the charger box and it says aways charge a marine battery on shore. I have electric at my dock and I have charged my pontoon boat and my bass boat batteries in the water for years. Does anyone know what this means? The kid at the battery store didn't know.