Description (From Recipaedia)
An electric battery used to power electric circuits. Will connect to any wire placed next to it and power it to a constant voltage, which is 1.5V by default. The voltage can be adjusted by editing the battery.
Crafting
Battery is made using 2 copper ingots and 4 coal chunks.
Use
Batteries are used to power electric circuits when another means is not desired. Place wire or wires on a block next to the battery and the circuit will be permanently powered by the battery.
When you are close enough to the battery and look at it, an EDIT icon will replace the CROUCH icon. Press this to change the voltage output from the battery.
Notes
Batteries are useful to supply a fixed analog voltage to a circuit.
They can be used where a voltage needs to be changed by the player's character.
Technically this should not be called a battery, however common mis-use has changed the popular meaning of the word. A battery has MULTIPLE electric CELLS. This is one CELL which may be used to make a BATTERY of CELLS.