One of the most important and expensive aspects of designing a mobile robot, is to find the right accumulator that allows long periods of autonomous operation. Most accumulators are quite expensive and modern accumulator technologies, such as LiPos (stands for lithium-ion polymer battery) or NiCd accumulators (stands for nickel–cadmium battery) demand for a specific charging device. In lack of both i was searching for a real cheap alternative to get a powerful accumulator in combination with a charging device that is able to fulfill my requirements.
So finally i came across my cheap accumulator drill set that contains 2 powerful rechargeable batteries with 18V with 1.300mAh capacity and a charging device for around 39€.
Combined with a really cheap L78xx voltage regulator we can choose the demanded voltage for any chosen consumer device.
In this case i had to power a Lego NXT brick, several Lego servos and additionally an Android smartphone device. As the Lego NXT brick operates on 7.2V i took a L7809CV voltage regulator to get 9V out of the drill accumulator (i already checked that the NXT brick worked with a 9V power adapter). You can see the PIN layout of L7809CV (78xx_datasheet) in following image:
Here you can see the direct integration in my Lego NXT Brick: