chargers

I have a 2008, Triumph 195CC with two batteries and the battery switch. I have seen it advertised that by plugging a solar charger into the cigarette lighter, the batteries can be maintained. If I plug a solar charger into the cigarette lighter, and have the battery switch turned to "ALL"...

Go solar? Is there a solar charger that really works? Please tell me the name. Otherwise, what I have is a boat with four batteries. Two in a 24v series, one starter, and one spare. How to charge them? I've seen so many bad reviews on various chargers I'm not sure which, if it exists, lower...