In this episose I power a camera and phone using a 3 battery batterypack. This hack is basically the next step after this. In this edition I've also added a meter to help in getting the contacts connected the right way around since this hack is aimed as a temporary, on-the-fly thing rather than a permanent hack.
Hooking it up backwards. On devices where the battery only fits one way, you can't guarantee that it will have electronic circut protection since it has physical circut protection. Because of this, it is extra important to make sure that you hook up the leads the right way. If you are doing something more permanent then this is less of an ongoing issue.
Wrong voltage, Intermittent/unclean supply. Modern devices are generally very forgiving, but as a general rule when working with these sorts of voltages, I try to aim within +/- 0.5 volts of the specified voltage of the product. Eg in this hack the camera and phone both require 3.7 volts and I gave them 3.6 (3 x 1.2).