1. Which cell it takes
Most digital calipers use an SR44 or an LR44, which are the same 11.6 mm button cell at about 1.5 volts. Some cheaper models take an LR44, and a few take a CR2032, so check the manual or the old cell.
2. Silver oxide lasts longer
An SR44 is silver oxide and gives a steadier 1.55 volts than the alkaline LR44. For a tool you rely on, the SR44 is the better buy, and it costs little more.
3. Zero it before you open it
Close the jaws and zero the display before you remove the battery. Most calipers keep their zero setting in memory while the power is off, but not every model does.
4. How to open the case
A small screwdriver, usually a 1.2 mm flat blade, releases the cover on the side or the back. Keep the screws in one place, and don’t force the cover, because the seal around it keeps out water and dust.
5. When the display fades
A dim or flickering display is the first sign the cell is going. Measure something you already know and check it against a rule before you rely on the reading.