Battery Sulphation solution
I looked at the DS500 Dedsulfator from Inovative Energy Systems. (Jack Rabbit Marine sells them) Very interresting; A little magic box that connects to the battery and sets up a harmonic frequency in the battery to break up the sulfation.
Some people swear by them. I''ve seen them in use but have no first hand knowledge of their effectiveness.
A good equalize charge will do the same thing.