The original 510 battery-box PTs are notoriously cheaply made, and all of mine died within a month or two, some taking USB ports out with them. I believe that their internal charger from the port draws too much current, both in terms of normal computer USB port ratings, as well as their own rating! I know Rocky Mountain Vapor stopped carrying them because of all the returns.
There are two PTs I really like and have used for quite a while now: the simple 5V straight-wire PT and the Hello Sit and Go, which is like a regular 510 battery with a USB port for charging. Its working voltage is 3.7V, and it seems to last off-line far longer than a regular 510 battery. The Sit and Go should work with any computer USB port rated for >300 mA, but I use a powered AC/USB converter. And the 5V PT needs an AC/USB converter rated to at least 2 Amps, but it is a great, and cheap, PT.