User serviceable parts inside: Replacing a smartwatch battery

When my Toq smart watch stopped accepting charge, and I was told I wasn’t eligible for a warrantee repair because I received it as a gift (seriously Qualcomm?) I figured I might as well try repairing it, or at least finding out what was inside.


Initially, I removed the 4 screws from the back of the main watch body and carefully disassembled the innards: main board flex daughter boards, display / touch screen and inductive charge receiver. I was shocked to find no battery present, however there were flex PCBs running off into the band. I’d wondered about the strangely bulky clasp before and prying it open with a spurger, I found a battery inside.

Unfortunately I was unable to find the exact cell / protection circuit for sale. So I sourced a lithium ion cell of similar capacity and form factor and soldered it into the flex circuit. However, the original battery had an NTC temperature sensor (not uncommon for cells far from their charge controllers) integrated into the protection circuit with a third wire going to the watch body and the battery would not charge without it. I guessed from common lithium ion standards that it was a 10k NTC to ground and soldered one in and it worked!

Unfortunately the new cell was slightly larger than the original so the back cover wouldn’t fit. One more sugru go the rescue.

With a little sculpting, I was able to make an unobtrusive replacement and restored my watch to its original functionality.