Batteries / Battery Power

When I first started out I used the normal Raspberry Pi power supply:

 but as I quickly found out, it is not enough voltage to turn the LEGO Mindstorms motors:

Then I figured out BrickPi had me covered:

That worked but I could still do better (by not using disposable batteries and having the battery last longer):

This is a remote-controlled car battery with a homemade adapter (the construction of the adapter will be in another post). The most important things were:

• the voltage is not above 12v (this would overload the Raspberry Pi) or below 5v (this would cause the Raspberry Pi to restart if the motors used too much power).
• the polarity must be correct (the inside of the connector is positive).
• measure the actual voltage using a multimeter (the battery marked 8.4v actually puts out over 10v).