Anyone who tells you that you can remove an internal CMOS battery from the motherboard of a laptop, and that will erase the BIOS password, has no idea what they are talking about. Why? Because the password is stored in an EPROM chip that doesn't require electricity to maintain the password. Why? Because laptops are portable, and easy to steal... and a BIOS password that could be easily removed by just disconnecting the time/date battery would not be much of a security feature. This is the stance that laptop manufacturer's take.
Now... if you have not noticed, if you enter the wrong password three times, you are presented with a code, and a space to enter a response code. If you call Dell Tech support, and pay the $49 off-warranty fee, and tell them the code you see on your screen, the tech will give you the response code to enter, allowing you into the BIOS to change or remove the password.
The other way to get rid of a Dell BIOS password, is to disassemble the laptop and remove the motherboard. Then, put the heat sink and fan back on the processor. Identify the EPROM chip that contains the password. Power the board, and short pins 1 and 6 on the chip. That means connect pins 1 and 6 with a short length of wire. Then reassemble the laptop. When it boots, you will need to go into the BIOS immediately, and take the CMOS from the pre-factory state it is now in, enter the service tag from the sticker on the laptop, then reboot. Your password will be gone.