Hi:
I am making a soccer robot (22cm in dia). There is no enough space for a larger battery. What I'm using now is a "Acid lead battery"(rechargable, 6V, 10x6x3cm).

The lead battery is too heavy (for a robot), so I am finding batteries that are:

Light;
5< Voltage < 9;
Rechargable;
Small size;
As cheap as possible (<300/each)

Sony's InfoLithium is one choice, does anyone know about the batt protect circuit inside the battery?

Stanley