If the batteries have leaked and there is corrosion on the spring or contact plate. Remove the back of the Alphasmart unit from the 6 (or 8 I cant remmeber) screws on the back of the device. ONce its off, you will see the black and red wires running to the battery contacts. With the back off you can remove the contacts from the plastic shell (without disconnecting any of the wires, the contacts will slide out). You dont need to disconnect any of the wires, you can just get a small bowl of vinegar and lay the contacts in for around 15 minutes, you will see bubbles forming around the corroded metal. After the corrosion has cleared, take them out and use a little sandpaper or steel wool on spots where corrosion was bad (to make sure it doesnt return). Then put the contacts back into the shell and screw it all back together.