Cob LED style flashlight questions

I found a cob style rechargeable li-ion light in the bin today at work, it raised my question why would they throw something like this away.
Took it home and sure didn't work. Plugged it in, tried it later without charging and it worked, but it was acting up after a while being unplugged and not working.
Took at the battery and it measured 4.0v, charged it up fully and discharged, capacity still useable, around maybe 450-600mah out of 748.

How come it acts up this weird ? I mean battery doesn't even warm up while charging from being discharged to 2.9v ( cut off pcb ).
It's a 14500 lithium ion battery, there are replacement batteries out there, no big issue if it just needs a replacement.

It sounds to me more like an issue with the electronics in the light than the battery. Intermittent function is more likely to be a loose connection or cracked solder joint than a bad battery.