I had a problem like this,
After it ran flat two days on trot, I ordered another battery....
But discovered the black wire on the charger to the battery, wih croc clip on, was in fact breaking down, so I spent out for nothing....
Also, leisure batteries all have a shelf life, the guy at pure freedom was telling me.
So if you've been unlucky and it Watson a shelf for two years before being sold to you, maybe that is what's possibly happened.
Mr B