21700 safety question

[SWF]

I have a pair of Zebralight SC700 flashlights and use Samsung 40T cells I bought from Zebralight. I keep these lights close at hand and use them briefly once or twice a week at most.

A couple of months ago I discovered one of the batteries was dead. I'd say it had been two to three months since the last charge. I put the battery into an Xtar Dragon and the charger showed the cell was at 0. I had read that total discharge was not a good thing for these cells, so I threw it away and inserted a spare Samsung 40T that I bought with the lights.

Now I find that both of my SC700 lights are out and the charger shows both batteries are completely dead. I decided to try charging them slowly, and after about 15-20 minutes the charger showed signs of life. It took a while, but both batteries came back to 99%.

Two questions:
1) What's going on here? I own eight Zebralight SC600 lights and I've never had an 18650 go dead like this.

2) Is it safe to recharge and use a 21700 that goes dead?

Thanks for any input!
Sam

 

[thermal guy]

Your SC700 must have a parasitic drain.

 

[DoctorMemory]

Your SC700 must have a parasitic drain.

And no low voltage cutout.

Safe to bring back from the dead? I imagine someone will tell us why it isn't, I've yet to see anything with my zombies but capacity reduction.

 

[SWF]

Thank you both for your input. I agree that parasitic drain is happening. I'd like to know if other SC700 owners are seeing this problem. I am now storing them with the tail caps backed off, but I've never had to do this with an SC600.