Most of the time when I charge my KR808-D1s I get the usual red LED on the USB charging widget and the blue tip lights up while charging. Once in a while, the tip doesn't light up but it seems to charge normally anyway. I can't seem to tie this to any specific charge state of the device -- ie, I've seen the charger widget LED go from red to the "almost charged" state where it kind of toggles red/green rapidly before turning green, yet the tip LED stays lit the whole time. And when I plug it in discharged to the point where the tip blinks and it won't draw, the tip generally lights. At first I thought it might be some kind of charge state indicator (ie, less/more than half charged) but there doesn't seem to be any pattern and it's not very frequent. It happens with both my standard and XL batteries. I don't know exactly what brand they are (bought from MyVaporStore) -- I think Kanger, based on similar products labeled as Kanger on other stores that sell identical looking products (stainless, XL and standard size, blue tip), but that's just a guess given all the cloning in the e-cig product world. No problems with any of my batteries, they all seem to hold a charge and work well, so I don't think imminent failure is an issue, either.