If you are observant, nature will speak to you. Listen to your cordless drill. What does it say? What does it say when you point the spindle at the sky, and pull the trigger and let the spindle turn freely? What does it say about drilling holes in wood or sheet metal? What does it say about driving screws? REEEEEEEEERRRRRRROOOOOOOWWW!!! The driver drives the load. The load loads the driver. The Phillips bit and the screw are lovers. So it is also with the geartrain and the motor, and also with the motor and the battery. Coupled together by copper and the subtle silicon, the motor and the battery whisper sweet voltage. They thrust current through willing wires, and push and pull against one another, bound together in a tumultuous embrace. If the battery is strong, as it should be if it has been charged recently, the battery's Yang will easily drive the pliant Yin that is in the motor. But just as day gives way night, and as the crest of a wave gives way to a trough, after much effort, the battery becomes tired. It's energy spent, the weakened battery's Yin will is easily overwhelmed by the motor's Yang. Do you understand? This is not a photograph. This is not a painting of a bowl of fruit. Life is dynamic. It is a dance. This is the way also with your cordless drill.