Not to be confused with the passive item, 9 Volt.
A silver battery with a lightning bolt on it.
Gives Isaac an extra charge every 15 seconds per room, up to a maximum of three charges. Using an item will reset the counter and let the player charge a maximum of six bars per room. The charging only happens as long as there are enemies in a room.
If used in conjunction with X-Ray Vision, this allows an infinite use of the activated item by running between incomplete rooms and the secret room. This can also be done with Dr. Fetus, Epic Fetus or Ipecac by blowing up the door of an uncompleted room and going in and out again. Using the Book of Revelations or The Nail for example can provide unlimited Soul Hearts. However, neither of these exploits will work in The Chest.
- 9 Volt - Allows for rapid use of held items.
Typically, the final (3rd) charge of the battery will be silent.
Additional item charges can be farmed at a rate of three item charges per bomb using the following method:
- Enter a room with enemies and wait for the battery to give you three charges. Enemies can be killed, but leave at least one enemy alive so that you do not finish the room.
- Exit the room using a bomb. Be careful not to kill the remaning enemies.
- You may re-enter the room and repeat the process as many times as you have bombs.
When worn, Isaac has the bolts of the monster from Frankenstein in his neck.