My Mini was second hand, so I don’t know what it was like new, but the back of it is very slightly curved outwards in the middle, so that the little hard feet don’t actually touch the surface it’s on and it will spin round freely if nudged with nothing plugged in.
So I’m wondering if this is a case of expanding battery. Does anyone else have this situation?
This certainly doesn’t sound right. Do you happen to also get the receipt from the previous owner, so you can send it in for repair?
I’ve had it for a year now from eBay. It’s very slight. Just slightly curved, enough for the feet to just clear the surface. I’m not sure about trying to get the receipt a year later, but it might be worth a try.
I’ve been wondering about what sort of battery it has and if it’s user changeable.
Mine also has a slight curve. I emailed polyend about it when I first got it last year and this was their reply.
"Thanks for picking up the Tracker Mini. There is normally a minor bulge on unit due to how units are constructed the plastic is shaped and fit together. It doesn’t cause any problems to the battery or any other part of the unit and everything is secure inside. The only time it is an issue is if the case doesn’t sit flat on a table; otherwise, there are no other problems. Let me know if you have any other questions and happy holidays! "
The first Tracker Mini batches showed indeed the back curved. I remember this QA issue was discussed in this forum and Reddit. The defect does not affect the tracker functions but makes it
more difficult to use it over a flat surface.
I bought mine only a few months ago, and the back is flat. Either Polyend figured out a fix for this issue, or I was simply lucky 
Thanks. I appreciate your reply. I guess mine is from an early batch. I wasn’t able to find this discussed here before, but I’ll look harder! I’ll also see if I can find it on Reddit.
Cool. Okay, so you’re in the same boat as me. That’s good to know. I’ll stop worrying about battery expansion. Thank you!!
Completely understand your being concerned. I would simply find some scraps of hard rubber or foam and use them as feet, glued on with a basic rubber glue, and they could be taken off and the glue cleaned off if they need to be removed. It’s the sort of thing I’ve done with various items.
Thanks. Yeah I think I have some unused little rubber feet that came with a pedal that I could potentially stick on the back.
