@Old_muel: I don't want to give dangerous recommendations to anyone. I'm not following this thread, I don't own a GH, just been summoned here by a fellow member to give my opinion on the state of affairs.
Li-Ion cells can fail in several ways. When they fail during charge, most often it's because the charger was out of spec (i.e. charged too fast, or didn't cut before 4.2V / wrong threshold value, or charged too long a struggling cell which then overheated and entered thermal runaway, aka venting + possible fire) This is why the first recommendation you will see everywhere is to never charge them unattended. Also a working charger might fail for some reason and yield out of specs conditions, so it's never 100% safe.
Then during use cells can fail if they get damaged, punctured or shorted, that's the most obvious cases and I don't think that's what happened here (unless for some reason this batch has physical defects in its insulation that can create a short condition say when you insert the cell in the device for instance) In the ubiquitous 18650 cell format for example, when you remove the insulating plastic wrap, you'll see that at the top of the cell the negative and positive regions are only a few millimeters apart and it's quite easy to short them.
But the more problematic failure case is when the cells are under-rated for the load they need to provide. Say if for instance they ordered cells with a 20A CDR (i.e. constant discharge rate) but the factory fumbled for one reason or another (bad batch, process failure, giving them B grades out of greed to save money, or any other reason really) and they only got cells able to sustain 10A CDR.
When you exceed the cell discharge rating, it will get hot while discharging and it will damage the cell permanently. This damage increases the cell internal resistance (IR), which in turn will also further decrease the cell CDR as well as making the cell voltage sag even more under load, it's a vicious cycle. In an unregulated vape you would immediately notice the poor performance, the vape would feel anemic or cold running. But in a regulated system it's even more vicious, the vape will try to make the cell work harder to compensate its bad performance and put more strain on it.
So if you notice a suspiciously short run time or if after a session when you remove the cell it feels abnormally hot (hard to tell in such a small device as everything gets hot in a confined space like that) I would advise you to stop using that cell ASAP. It might work for a while but as the cell deteriorates it will run hotter and hotter. When it reaches about 120°C during use it will enter thermal runaway and it's game over... for your hand, your face, possibly your house and your belongings due to the fire... or worse.
. So lucky to have a great vape shop to rival any other around the world. Customer service at its best. Thanks Adam and the crew.
