FYI, I was charging the pen battery on my laptop when it gave out a surge warning to the USB port and shut it down after about... 30 minutes or so charging it up.
I suggest as a precaution, making sure if you charge from your computer, that you have the newer USB ports that detect the surge and will shut it down like mine did. It could be a fluke, could be something that damaged it in shipping but it definitely won't be going into my wall.
I'm charging my phone on it now (my phone has the warranty protection on surges for charging, since I live in Florida and lightning likes my house) and no issues, but something to watch out for. It's getting a tad warm charging my phone - which it really shouldn't be doing so take caution if you intend to use this in a purse or bag and want to charge with your phone/tablet in hand. Make sure you take it out to cool it every so often.
ETA: After running through a full charge, it gave me about 40% battery, which seems rather underpowered for the size, but will certainly get you some extra life for not a lot of effort!