When its on battery power, the battery gets heated up and develops the internal short.... I watched somewhere in the youtube, someone suggested putting the battery in a plastic bag and then in the freezer.... I have not tried it or endorse such method though...
If you constantly on battery power, of course, the life will be depleted as well....
The recommendation meant, if you always on AC line, take out the battery from its compartment.... and put it back when you travel out...
It's time to buy a new battery.... too bad.