Thrunite TH30 and battery help

[Sarratt]

When I try to use a freshly charged cell in my TH30 it flashes once and seems to shut down.
I'm only charging using the light itself and the only other cell I've used are Nitecore 3400 mah 3.7v 12.6WH

However when I run down the cell in another light a bit it can then be used in the TH30.

Is this normal ?
What is causing this?
Is the light itself overcharging the cell?
When I do get a proper charger for 18650's how will I know how much to charge each for use in this light?

Thanks for any help.

 

[Marquis07]

This is late, but I had the exact same issue with my tc15 and multiple th30 s. I found that if I plugged any of the lights in for a second, they would reset the cell. I ended up using samsung 30q cells instead.