I had a leisure battery failure similar to yours, I took it to the place I purchased it from and they did a voltage drop test, after I had charged it overnight it was just losing charge as he tested it.
It was approx 4 years old, I was told that 4 years was a good life expectancy from a leisure battery, bit the bullet and bought a new one problem solved.
Have Fun
Malc.
Malc
November 2010