All about the Roland Jupiter-series

Damn !!!
This is the third time I have to let the music-shop put a new battery 
in my Roland Jupiter8.
My Jupiter8 loses all it's memory when it's power has been off for 2 
weeks...
Is this normal?
Aren't there better batteries available who last longer and won't 
lose it's memory after 2 weeks?
It's a real hassle as I'm afraid to fix it myself.I'm a real idiot 
whith a soldering iron.That's why I have to take my Jupiter8 to the 
music-shop and this keyboard weighs a ton!!!
Please help!