I forgot to mention here - All you are doing when you switch this jumper is you are crossing wires. think of it like this - you stuff two wires into your wall plug and touch them together instead of making a circuit (well, technically this is a short circuit so it is still a circuit - but you get the idea). This 'shorts' the entire circuit (battery included) and clears the CMOS. Of course, your MB is going to be using DC in this case, but I am trying to get you to visualize it.
Chances of actually causing battery fail is low however, but if you do it enough, you will definetly kill the life of the battery. There is a ever so small chance of overheating and making the battery either leak or blow up though - but it is minimal. You'd have to short it for a while longer than the 10 seconds recommended I'd bet.
The short answer - if you want your battery to last a long time - like the life of the motherboard, remove it before doing this. Overclockers probably need to worry about this more than anyone though.
-S
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