I've been using DSE901 for about 7 weeks now, right from the beginning I've been charging them exactly 3 hrs (that's what my manual says) and alternate between 3 batteries and each lasts me at least 6-7 hrs and I do vape quite a bit, when the blue lite flashes 25 times I get no smoke, I know it's time to charge... Vaping with fully charged batteries is another pleasure, it's more productive as it produces maximum vapor possible.
I do worry about forgetting them on the charger longer than 3 hrs, I fear they will all drain back!!! Can anyone tell me I'm wrong on that so I stop worrying about it cos I'm the same with charging my mobile phones (always charge them for exactly as long as necessary)..
I wouldn't worry - I always leave one on overnight for 7-8 hours+, and they seem to hold as much charge as when they were new. I don't get 6-7 hours out of them, but then I chainvape all day. I quite often swap batteries before the one I'm using is flat, if another has finished charging, and this seems to do them no harm either.