I don't think that most people have not really touched on your problem. I think that your charger is dead! With a dead charger it does not matter what shape your battery is in or what you use....
Get a new charger! Before replacing the old charge (and someone did mention this) ensure that your system does not have a short circuit. Get, borrow, (temporarily steal from your car) a battery that you know is charged. Disconnect the battery in the boat, turn off all
electrical and
electronics on the boat. Using a set of jumpers connect the known good battery, if there is a spark you need to look for crossed
wiring or a short circuit somewhere. This needs to be dealt with before doing anything else.
If there is not spark, start turning on devices 1 at a time, only every having 1 device on. If they all
work then you should be okay replacing the charger and once the battery has charged (let it fully charge) you can then start using the devices again.
As long as you have the boat battery disconnected it might not hurt to take it to a garage or a store that does batteries and have them test it to ensure it's is working well.
Good Luck