Tandem t:slim battery problem

I had a strange and a bit unnerving event today.

I was out and about (but maintaining proper social distancing :slight_smile: , mostly outdoors, wearing my heavy winter coat.

I got back home, and for some reason (I normally don’t worry too much about this) checked my Tandem t:slim pump battery. It read 40%. Normally I wouldn’t do anything at that level, but would let it go for 2-3 days at least. But (again for some reason) I decided to let it charge up while I was at my computer. I plugged it in (to my powered USB hub, not the official Tandem charger, but that’s always worked in the past). A minute or two later I checked it, just to be sure (and I may have gotten a little vibration). Behold and 'lo, my power level was down to 5%!

I left it as is, and it started charging, though it seemed slow. At the 20% level, it gave me an error message, saying the source in use was not sufficient (which was new). I changed to the Tandem charger, and let it continue. It did charge up to 100%, and now seems to be holding its charge as usual.

I called Tandem Support, and the tech was quite agreeable and friendly. She said this was rare, but sometimes did happen, especially during times when the power drain was high (e.g., giving lots of alerts). There is an internal power level used by the system, and it’s not the same thing as the power level displayed on the screen! (Yikes! What good is the screen display version?!) She helped me investigate, and sure enough, the pump had been giving me “Low power” alerts all afternoon, which I never heard or felt (through my winter coat? but I usually feel the vibration). She suggested I should try charging it up 10-15 minutes every day, just for forestall such events (other users do this, she told me).

This is a bit scary! Why does the pump sometimes not show the correct power level? That “40%” was obviously bogus. Has anyone else encountered anything like this? Or know more about what was happening?


I have not had this issue however I carry a cheap 10 dollar battery charger in my car. I leave it charge up all the time till I need it and the charger is the size of a cigar so I can take it anywhere. I have another one in the house.
It charges up fast and I get 4 or 5 charges off it.

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@K_Hjalmar you should call Tandem tech support back. I also had this happen, it’s a sign of a battery fail. It’s probably going to get worse and you will need to get your pump replaced.