Yes, DL and you have to play around with the settings. Its basically the opposite of overclocking. Here is a tutorial. Its for a Pentium M but should work for you.

http://www.notebookforums.com/thread70943.html
http://www.nordichardware.com/Articles/?skrivelse=465

Undervolting wont do anything for you current battery. But it might help with your new one.

BTW, there is also a store in 4th floor Vmall that does repacking. Another store in ground floor ST Francis square does the same thing. Might be cheaper than replacement bat.