9 Volt

Effects

Fully charges the current activated item upon 9 Volt's first pickup.
If the current activated item has a recharge time of more than 1 bar, then it will grant 1 bar of charge whenever the item is activated.
If the current activated item has a recharge time of 1 bar, then it will change the item to have a timed recharge of 15 seconds. The recharging of the item only triggers so long as there are enemies present in the room in any fashion. Empty rooms do not cause recharging to start.
- An enemy spawned in a cleared room will also cause recharging to start.
If the current activated item has a real-world unit-based recharge time, 9 Volt now makes autocharging items start at half charge instead of empty, allowing quicker reuse.
(Added in Repentance) Causes Isaac to emit a bright glow in Curse of Darkness rooms.

Enemies generated through a (Slot Machine.png) Slot Machine, (Shell Game.png) Shell Game, (Added in Repentance) (Hell Game.png) Hell Game, (Added in Repentance) (Rotten Beggar.png) Rotten Beggar or breaking Urns/Skulls will restart the charging process, even though a cleared room still counts as cleared if enemies are spawned in it.

2-bar items: Fills the entire gauge in a single room, effectively granting the opportunity for the item to be used every room.
(Added in Afterbirth †) 3-bar items: Quadruple rooms and L-shaped rooms give 2 bars after clearing them, allowing one free use of the item in those rooms if the gauge is full upon entering them. It can also be used at the beginning of a Boss Challenge Room to get the full charges back after beating both bosses.
(Added in Afterbirth †) 4-bar items: In a Challenge Room, if the item is used during the first wave, it will get all its charges back at the end.
- (Added in Afterbirth †) (AAA Battery) AAA Battery + 4-bar items: Same as the 3-bar item synergy without AAA Battery.

9 Volt: No further decrease in charges.
(Added in Repentance) Alabaster Box: No effect.
(Added in Afterbirth †)(Dim Bulb) Dim Bulb: Prevents Dim Bulb from working, as minimum charge becomes 1 instead of 0.
(Added in Repentance) Everything Jar / (Added in Repentance) Larynx: The first bar gains an automatic recharge, but the further bars will not be affected.
(Removed in Repentance) Sharp Plug: Renders the Sharp Plug unusable on 2+ charge items. Sharp Plug can only be used if the item is at 0 charges, but 9 Volt instantly gives +1 charge to the item upon activation.
- (Added in Repentance) Lowers the cost of using Sharp Plug by half a heart on 2+ charge items.