The CMOS battery on this model of laptop (as well as most laptops) is not user-serviceable and, as such, is not easily accessible. With most Acer (and other cheaper) laptops, they are soldered into place, partly out of laziness by the manufacturers to design proper battery sockets but also in an attempt to discourage end-users from trying to fix their own machines. As such, the only way to pull the battery would be to disassemble the machine, desolder the battery, and then reverse the process. This is not something for the timid or the average soldering iron.
To work on circuit boards, one must use a low-wattage iron or else he will burn the circuit board, requiring replacement of the board as a whole.
My professional advice to you is to send the machine in to Acer's repair center to have the password removed. They have the software that will accomplish that for you without any danger to your hardware.
As for the possibility of the hard drive being locked, be aware that we are talking about a low-end Acer laptop here, not something utilized by the Pentagon. Thus, this is not truly a concern. What's more, the only type of security that would exist on the hard drive would be circumvented by reformatting and reinstalling Windows and anything else you have on there.
I hope this information helps. Let me know if I can answer any other questions for you.