Hi I just posted a seriously similar thread for the record I think it might just be extremely slow..... I have not gotten any reply about how long it should take to charge but you average PC USB port only provides 0.5A this might mean it might take 2-6h to charge since the average wall 0.5A charger take that long from what i've read.
Everyone seems to have a external battery charger i'm not 100% sure why but i think its because onboard charging times are just too slow and everyone is paranoid about battery exploding, I would have thought the chance of something going wrong while charging would be similar to the chance while discharging so the idea that you should charge externally seem a little ludicrous to me if you happy to
vape on that same battery.
For the record you can apparent get USB chargers that have 2.0A of current and the
dna PDF says it can handle up to 16A..... so i assume 2A is fine which would speed up the charging time that said most external charges i've read about have a trickle charge period so the straight up 2A may reduce battery life......
One last thing I'm no Battery expert please check with a knowledgeable person before pushing 2A through the USB charging port....... this whole post is simply peculation nothing more so only take it as that please!