Just be sure it is marine certified
The important point is that whatever charger you purchase and install, it must be a unit that is designed for marine use.The difference isn't just a rust-resistant case, or a higher price tag, but a design that isolates the 12V output from the AC input. This feature is CRITICAL to your safety and the safety of others docked around you. In addition, the integrity of your boat's underwater metal is at stake. An improper 'automotive-type' charger can cause severe galvanic corrosion of your (and your neighbor's) underwater shafts, thru-hulls, struts, outboards, outdrives, etc.A case in point. A friend of mine took his powerboat to Florida last year. He docked it at a marina, plugged in to keep his batteries charged, and returned north for the holidays. After 5 weeks he returned to Florida for the rest of the winter. Shortly after returning he noticed that his boat had a unusual vibration under way. When he dove on his running gear, he found that both of his props ($800 each) and his rudders were damaged from corrosion. In fact, his props were a total loss. The metal was so attacked that he could snap off the tip of the blades with his fingers!He eventually found that a live-aboard sailboat several slips away was using an ordinary extension cord to power a battery charger. The cause of this damage was still hard to prove and it cost my buddy close to $3K to put everything right again.Being afraid to leave his boat in the water, he hauled it and stored until time to come back north. He never got to use his boat all winter. A real horror story.If cost is an issue (like when isn't it...), look for a used charger, one too small for someone else-perfect for you). Just make sure it is a MARINE unit.Hope this helps.Rich