Ok ...question ...can you open the case or is that to technical....no offense ment..but if you not handy then the $35 you might get charged could be worth the fustration....
If your not that bad.....
unplug all cables ...so the computer is just the box
put it on a comfortable table with good light peferable a wood char/ wood or cement floor...
remocv the case....could be screws, latches.... could come foward come backwards or go sideways...had a dell that you lie on its side and open it like a case...
before touching ANYTHING ELSE ....TOUCH something metal...to discharge static electricty
then lookinside the case...for a silver wafer(watch battery) when you find it.....touch metal again....if you zap you system your going to be misarable...
using an eyeglass screwdriver (flat one) carefully...did I say carefully lift up the battery....then remove it...wait did you touch metal....
now...after touching metal...never can be to safe

pop the new battery ...usally but not always..RS232...back in
then revese the steps
real easy to do...in most cases