4.5 Volt

4.5 Volt is a passive item added in The Binding of Isaac: Repentance.

Effects

 * Causes Isaac's active item to charge when Isaac deals damage to enemies, rather than when he clears rooms.
 * Damage dealt by active items work as well.
 * Charges are gained at a rate equal the following formula: (40 + 20 x stage). For example:
 * In I /  I, it takes 60 damage to gain 1 charge.
 * In II /  II, it takes 120 damage.
 * In I /  I, it takes 180 damage.
 * In /, it takes 240 damage.
 * In, it takes 300 damage.
 * Ascent floors use the values of their regular floors, meaning the amount of damage 4.5 Volt needs to gain charges steadily decreases during the Ascent sequence until reaching Home.


 * Multiple charges cannot be gained at once.
 * Overkill damage does not count towards a charge.

Synergies

 * Increases the rate of charge by appending its 15-kills-per-charge quality on top of 4.5 Volt's damage-based charge.
 * Door Stop//any means of room resetting (Infinite bombs) : Provides infinite charges by clearing some enemies then leaving the room, and repeating.
 * The item in the second slot gets charged when the first one is full. Overcharges on the first item also jump to the second one.

Interactions

 * Does not charge items which gain charge over time by default. (e.g., , etc.)
 * Items converted to charge-over-time by are not affected and may gain charge in both ways.
 * : No effect. It still must be charged with Soul Hearts.
 * Dim Bulb: Does not deactivate until the first charge bar is completely filled. A partial charge of the first bar will retain Dim Bulb's bonus.

Trivia

 * The Game files names 4.5 Volt's icon as "assaultbattery"
 * Assault and battery is the combination of two violent crimes in common law: assault (the threat of violence) and battery (physical violence).