Most Dell system passwords are not stored in CMOS memory therefore are not blanked by removing cmos battery. Usually they have been stored in non-volatile memory chips ie. retain their memory regardless of whether power supply is present or not.

You can find a lot of info on the web on this by doing a google search on 'dell 24c02' or 'dell 24c04' - the 24c02 chips are usually in older dells and I have found the 24c04 in the later model dells like the inspiron 8600
depending on the model as to where the chip is located. Shorting the correct pins on this chip will remove the BIOS password altogether. Although if you are not confident of taking apart a laptop then I would advise against this as I have quite often had to completely dissasemble units to get at this chip.