review of the Accutire MS-4021b tire pressure gauge, you may also be interested in how to change the battery. Changing the batteries inside an Accutire MS-4021b tire pressure gauge is easy. You'll need:
A Phillips screwdriver (I used a PH1 sized bit and it worked fine).
3 new LR44 batteries to replace the old ones inside your gauge. These batteries are also called A76, 357, or AG13 and are 1.5 volts each, making for 4.5 volts of total power.
Just line up your three new LR44 batteries like the inside of the compartment shows and squeeze them into the metal battery holders. Then screw the battery compartment cover back on. Piece of cake!