CR2032 3V Lithium watch style batteries are heavily used by the bike industry for a number of devices. Head units, basic bike computers, transmitters, and heart rate monitors all come to mind. About the size a nickel, it's flat profile makes it a favorite of companies like PowerTap/CycleOps, Garmin, Lezyne, Wahoo, Cateye, and so on.

Always verify which battery type and power you require. Most lights or computers will list what battery is used on the battery cover or casing of the device. The easiest way to identify is remove your existing battery and examine the markings. Always handle the exposed new battery carefully, and avoid touching the bottom (considered the negative pole, usually unmarked) side that contacts your unit. Oil and moisture from your hand can lead to corrosion or poor transmission.

When removing and installing battery, carefully check to make sure any retention clips and seals are properly used. For optimal use and proper moisture protection, the battery cover will generally close firmly, with some minor effort.