I know this is a little dated, but fount it when looking for a tear down thread to try to fix mine later....
The 510 connection is the weakest link... Well, if you are rough on it. With out thinking about it, I used to keep my cartos screwed in when pulling my tanks off. This cause the 510 connection to become loose over time, and as of today it quit firing. I used to be able to wiggle it in to place and it would work again, but not this last time. Also, With in the first month I had it, I had the device and a charging cable in my bag I take to the office. I smelt buring wires one day when I set it on my desk. I had forgot to switch the output off when I was using it to charge my cell phone. Guess that kept the USB plug pretty acitve, and while sliding around in my back pack, the micro USB end got lodged insite the USB port and was burning it up lol. Smelled pretty bad, but worked without issues for 6 months until the 510 gave.
Long story short, no doubt this thing would have lasted me a year had I not been so rough on it, and it still might as long as I can get the case open. If I can't fix it tonight, I fully plan on ordering another one. Just the battery life alone is a selling point, most of my other mods just sit now.