LR44 button type lithium battery
LR44 button type lithium battery used commonly in small items such as cycle computers or sensors. The picture below shows two batteries so that you can see both sides for information purposes. This product is priced per single battery.
The LR44 is much smaller than the CR2032 battery, another common button type battery used in mini bicycle lights and cycle computers
Lithium button batteries are very dangerous to children, if swalllowed can result in death.