What is the difference between mains electricity and battery operated electricity?

Batteries range in output voltage from 1.2 volts for an AA rechargeable, to 12 volts for a car battery. There may be other voltages, for special purpose applications. Batteries supply DC (direct current), meaning that the current will only flow in one direction.

What is considered "mains" electricity (from a plug or receptacle in the wall) is alternating current (the current is oscillating between flowing one direction, then the opposite direction then back and repeats). It oscillates at 50 or 60 times per second, depending on what country you live in. Also the voltage is between 100 volts and 250 volts, depending on the country, as well. These features enable the voltage to be changed up or down rather easily with transformer, and allow the electricity to be transmitted over long distances.

But the alternating current and higher voltages also make your mains electricity much more dangerous to touch than a battery. A person's skin has pretty good resistance to electric flow, especially direct current. But with alternating current, if you touch a wire, charges can actually form under the skin and start flowing through your body, because your skin acts as a capacitor. Then, the oscillating current back and forth through your organs is much more damaging, possibly causing your heart to stop pumping.