ah yes the F***ing CMOS battery. yes I know where that little sucker is. I use bad language because I tried to get at mine, unscrewing nearly every screw in the damn thing, only to strip the last screw necessary to get at the CMOS battery, and fail to remove it. It is a major pain to get at the CMOS battery. It is under a little metal plate under the left palm rest.
I wish I could tell you it is as simple as removing the keyboard to get at it. It is not. You basically have to remove every screw you can find. take care of keeping accurate track of all the screws where you removed them from so you can put the thing back together. At least it is possible to disassemble it to that point without damaging it.
download the service manual if you have not already. do a text search for CMOS, and it should give you some guidance. See figure 1-7 showing the location of the CMOS. you have to remove the whole bottom case to get at it. you wont be able to get at it from the top without removing the bottom case. sorry if this is confusing. The worst part about removing the bottom case (following the step by step in the manual), is it is necessary to disconnect the monitor ribbon cable and the keyboard ribbon cable, and maybe one more). there is a little release switch on the ribbon cable connection to the mobo that allows the ribbon cables to slide in and out easily. it is kind of hard to see it and the manual says nothing about it. if you can't find it let me know and I will try to describe it better.
my heart goes out to you. it is a several hour project to replace the CMOS. bar family and friends from the room where you will be working and clear a nice large work area for all the parts. prepare for the worst and think up plenty of swear words to have them at the ready as you cuss about how unbelievably difficult this is.
be careful on those last 2 screws holding the plate in. they are cheap and strip easily. good luck putting humpty back together again if you actually get to and replace the CMOS. Oh, and the CMOS battery is actually glued into place so you may want to think about how you will glue the new one down.
