Removing the cmos battery on it's own won't help. You will also need to remove the main battery and the mains connection. Sometimes 2 minutes will be enough although some systems will require a few hours, if not overnight.
Check your motherboard manual or call Compaq tech support (I hope you have lots of time and patience). If there is a CMOS jumper for removing the password, one or the other will tell you where it is and how to clear the password.
Power-on passwords on laptops generally cannot be removed by disconnecting the battery, nor is there an accessible reset jumper like you find in desktops. They are made that way to deter theft. Call the manufacturer and be prepared to provide proof of ownership before they will help you unlock it.
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