The Pismo has an internal PRAM battery that, when fully discharged, prevents the rest of the computer from either charging or even starting up......that battery is much smaller and separate from the battery that slides into the side of the computer to power the whole thing.
Your best bet would be to lift the keyboard and remove the hard drive physically in order to clear it (by installing it into an external enclosure and attaching it to another computer).....or by simply smashing it with a hammer.
As I recall, the capacity of the hard drive in the Pismo wasn't all that big (somewhere between 4GB and 10GB were the original installed sizes)......unless you replaced the drive with a much larger capacity HD somewhere in the far distant past, you won't be wanting to keep and re-use the hard drive for any other needs.
FWIW, my original Pismo has been so far modified as to have a full GB of RAM, a 120GB internal hard drive, a DVDR slide-in CD/DVD burner, and an internal 802.11G WiFi card......and the damn thing still works! I quit hauling it around with me when the 1.5GHz Aluminum PowerBook G4 replaced it at nearly half the weight and 8x the speed......and IT still lives on my shelf fully functional as well!
My early 2009 PowerBook (the last model with an externally changeable battery) is populated with 6GB RAM and a hybrid 500GB/6GB SSD that runs so fast that I can't justify moving to any of the latest release portables......and so it goes.
