18650 cell damaged during a fall?
 

My Trustfire flashlight rolled off the kitchen counter and smacked the stone tiled floor. I picked it up, hit the power switch, and nothing happened. Swapped out the cell for a fully charged one and the light came on. Drained that one to the point where it needed to be recharged and charged them both.

The charger indicated green on both cells, but the light only comes on with the one cell.

So can a sudden impact affect a protected Li-ion cell? I guess it can, but is there any way to repair it?

Yes it can, the protection circuit is stamped onto the cell - a shock can loosen the tab.

Also, it's a bad idea to charge mismatched cells in parallel. You could get away with it using NiMH cells, but Lithium-ion is very unforgiving due to the rapid chemical reactions that can take place and the much higher energy content versus NiMH. Drop the damaged cell off at a battery disposal unit (Home Depots here all have one) and don't attempt to repair it - if that cell shorts out inside a flashlight, you effectively have a pipe bomb.

18650 cells are cheap, don't chance it by continuing to use it.

Does anyone even make a charger that use one circuit like the cheap Nimh chargers? The Xtar WP2 charger I have charges two batteries on independent circuits.