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.
Notes[ | ]
Tainted characters with active items in their pill/card slot will not have those items charged by 4.5 Volt if their active item isn't already fully charged.
Lilith can be particularly strong with 4.5 Volt during long fights such as Delirium and Hush, especially if she still has the Box of Friends, as the damage she deals will allow her to repeatedly duplicate her familiars, dealing many times her typical damage during a single fight.
Bethany will benefit from 4.5 Volt's effect for regular item charges while retaining her ability to use Soul Hearts as item charges. This applies to Tainted Bethany with her Red Heart charges as well.
Tainted Jacob will gain charges from 4.5 Volt when Dark Esau damages enemies.
While the two versions of Tainted Lazarus normally charge both their active items at the same time, 4.5 Volt will only charge when the state that holds it deals damage, and will prevent it from being charged when the other clears a room. This makes 4.5 Volt much worse while playing Tainted Lazarus.
Synergies[ | ]
Book of Shadows: With sufficient damage, the Book of Shadows can be kept active indefinitely.
If combined with 9 Volt, it becomes even easier to achieve invincibility.
Door Stop / Mercurius / any means of room resetting (infinite bombs): Provides infinite charges by clearing some enemies then leaving the room, and repeating.
Jumper Cables: Increases the rate of charge by appending its 15-kills-per-charge quality on top of 4.5 Volt's damage-based charge.
Old Capacitor: Since the 4.5 Volt also makes it so that active items don't charge when clearing rooms, this trinket can be picked up with no downside.
White Pony: Since the beam trail from the charge attack deals so much damage, if used on a boss with a high amount of health, 4.5 Volt will often completely recharge the item after each use allowing for repeated usage while the boss is still alive.
For the same idea (so much damage against bosses that the active item is recharged from its use),Tammy's Head + Brimstone / Azazel / Tainted Azazel is also a strong synergy.