In the second picture here in the article, you can see the (only) cable that goes from the unit. It comes out of this eyelet/loop on the inside of the right arm where the control buttons are. In another picture you can see what the charger looks like. When the battery is charged, you can of course use it without the cable.

The answer above is correct, there is a piece of cable hanging out on the inside under the control buttons and this is connected to the power supply unit supplied, mine is called: Innov Model Type IVP1280-2000G. It supplies 12.8 volts DC at 2.0 amps. The positive pole is in the middle and the ground (minus) is on the outside. This information can be used if another power supply unit is used. However, it must be connected to the power supply for at least 12 hours at the beginning.