Special chargers for marine batteries?

I think maybe what they very poorly were trying to say is that the standard charger is not intended to be used as an onboard charger. They have fans and such that could generate a spark, which would not be good in an enclosed area with potential for gas fumes.

I found this at on the lake.net.
Most chargers that are designed to charge you car batteries are not designed to charge your boat batteries: they just don’t always completely shut down. And how often do you think that you can remember to unplug that cheap charger when things “look about right?” From what I have read, a 3-stage charger – one that will totally shut off when the battery has reached full charge – is your best buy. Without all the chemistry and physics involved, batteries will do best on a regulated diet of amperes and volts served up in the right amount… and in stages. There are three stages: 1) bulk, 2) absorption and 3) float. The bulk stage is where a battery is brought up to about 75-80% of capacity. Absorption is where the voltage is constant but the amperage is tapered while the battery is “topped off.” And finally, the float stage is where the voltage is just enough to keep the battery from losing any charge. I’m sure that you are aware of this, but a battery can lose – depending on how and where it is stored – up to 30% of its charge per month – just sitting around the house or garage! And there are all kinds of things that affect battery charge and loss thereof (like temperature, humidity, state of discharge, age of battery, etc);

I recently prurchased a battery charger for use around the house. While reading the manual I noticed that it specificaly said "not to use on marine batteries, marine batteries require a specific type of charger". Can anyone tell me about these special marine battery chargers are and have I been unsafe or risking damging my boats?