Tutorial for replacing the battery of your Alivecor Kardia Mobile 6L ECG
At the back of your unit is the third electrode of your ECG.
Use a small screwdriver to carefully remove the 2 micro-screws.
You will find a CR2016 lithium battery that you can easily replace.
It's quite simple and you won't need to do it often because the battery can last more than a year (depending of course on the frequency of use).