I am having a problem with an 18650 battery I use on a LED hunting light . It takes a full charge on the charger and when I first begin to screw on a tail pieces ( I have tried a single click, double click and a and pressure switch), the LED light illuminates. BUT – As the tail caps are seated fully it fails to illuminate. I have a second battery and it works fine. I have tested continuity in the tail pieces and it is operating as designed.

Question – is it possible that the contacts inside the 18650 cell fails when the pressure of the positive contact against the LED emitter spring and the tail piece post compress the cell? I am not familiar with this type of cell but this is what I am diagnosing as the problem.

I'm not 100% familiar with them, but LI-ION 18650's have an internal circuit board to prevent overcharging and over-discharging.

It could be that applying pressure is causing the board to compress and a crack to from making the circuit fail, hence the entire battery to fail.

Given the price of these batteries on sites like dealextreme.com, I'd just buy two more and throw this one out.

I already ordered more ...it makes sense that it would be the board flexing. Thanks for the intel.