The Joye eGo Pass-Thru is a 650mah eGo battery that has a screw off bottom. This reveals a port that can be plugged into any USB port using the cord that comes with the battery. This not only allows you to charge the battery but also to use it while it is charging! When it is done charging you can screw the end back on the battery and use it like normal. It has an indicator light that is red when charging. This is a must have!