For your convenience, one replaced battery in less than 20 minutes. 
https://files.catbox.moe/xsb6gi.mp4
>>389213702
Cant say for sure, they were a friends they used for a long time. He said he used them plugged in to batteries all of the time which i think lead to them dying sooner. I'd guess way more than a 1000 hours on them. From my experience of one tracker that I had for my hip, I have two years on it now, and its only now starting to show its age, but I've been charging it conservatively. Even so I still get 4 hours on it. The new batteries should get around 4.5h. 
>>389215058
no idea
>>389206554
forgor to mention that this is the hardest part. The USB board sorta snaps in. and its tricky to get the screw driver around the inside piece.