Under Armour HEALTHBOX Guia De Inicio Rapido página 12

Replacing your UA Heart Rate battery
If the power on your UA Heart Rate is low, the blue light will not
turn on. For optimal performance, replace your battery as
described below:
1. Using a coin, open the back battery compartment door on your
UA Heart Rate module.
2. Remove the old battery and insert a new battery (CR2032).
3. Secure the battery compartment door back onto the UA
Heart Rate module.
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