18650 batteries working, but died after charging

I had two 18650 cells in a flashlight. It had hardly been used but about 20 to 30 times for short periods of 5-10 minutes each time over the course of about a year. It was still bright, but I decided it was time to top it up with the supplied two cell charger. The batteries have printed on the side that there is internal short circuit, over charge and discharge protection - pretty nice I thought. After about 30 hours of charging, the red light still did not turn green as it should have to indicate fully charged.Istopped the charging, put the batteries in the flashlight and nothing! I measured the voltages ofeach cell and they were 0.0V and.034V - pretty dead!

I measured the charging unit and it registered at 4.2V, which matched the label. That seems OK.

Anyone have an idea what happened to these batteries and could they be resurrected somehow?

It sounds to me like that the cells were weak, and the charger just pushed them over the edge. I'm thinking that there may have been dendrite build up in the cells. When the charger kicked in, there were shorts inside the cell and killed it all the way. It's possible the cells that you have were cheapo cells not worth much to begin with; so this kind of exasperated the condition.

Probably were "cheapo" cells... high power light, 2 cells, charger for around $10...what can you expect?

Can also be the CID that popped due to issues. Neither less throw them away and crosscheck so your charger doesnt overcharge

I think that maybe these cells were a kind of ultracapacity 7500mAh super ***Fire* cells, and possible to be considered as a "fake" cell. with maybe some sand inside.

there are some youtube video's about 'what's inside those fake ultraFire 18650"

best regards

Stefaan

Most fake cells today actually dont have sand in them. I have not seen 1 so far having that.... I have opened a few (Done videos for it too)