I think its personally because i'm a bit bad, but i just had a run where in the first boss fight plum spawns and even with two B.bobby i don't have time to stop him and i waste a charger.
I suggest that at the start of a boss fight the enemies that are spawned are a bit after the boss gets up.
Also the charger replacement is a bit expensive so it makes it really frustrating to lose one and sacrifice discovering new items and "deck building".