Pull out when charge goes up (4)
I believe the answer is:
draw
'pull out' is the definition.
('draw' can be a synonym of 'pull out')
'charge goes up' is the wordplay.
'charge' becomes 'ward' (I've seen this before).
'goes up' says the letters should be written backwards.
'ward' in reverse letter order is 'DRAW'.
'when' is the link.
(Other definitions for draw that I've seen before include "Design" , "Extract" , "Collect one's pay" , "2-2 in game, say" , "attractive thing" .)