My UTi260B has a failed, taking forever to charge the battery and it does not turn on. This might help owners with similar symptoms.
This appears to be a common problem.
Uni-T have done what they can to make it difficult to get into the case, eg to replace the 26650 LiIon battery, Uti260B teardown might be helpful.
Powering the device from a regulated power supply instead of the battery, it draws 1.2A while the power button is pressed, and returns to zero after the button is released… but it does not power up.
I have seen reports of UTi260B damaged apparently by rogue chargers that subject it to excessive voltage. I did find a TVS (SMBJ28CA) across the DC input, but since it triggers at nominally 28V, it is useful only as reverse polarity protection. I removed the TVS lest it was damaged (it gets hot) and the symptoms are just the same.
This has been such a poor instrument to use, I will not waste more time on trying to repair it, nor would I think of replacing it with a Uni-T brand product.
It seems that most if not all product in the market has a lifetime battery, not replaceable by the end user, and the battery determines the instrument lifetime.
My quite old Fluke VT02 which uses 4xAA alkaline cells is still working, not as good in feature as the UTi260B, but easier to use… and it still works, and has user replaceable batteries, no tools required.