Battery units? (5)
'battery units' is the definition.
'cells' can be an answer for 'units' (cell is a kind of unit). I'm unsure of the 'battery' bit.
'battery units' is the wordplay.
'battery' becomes 'C battery' (C battery is an example).
'units' becomes 'ells' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'c'+'ells'='CELLS'
Can you help me to learn more?
(Other definitions for cells that I've seen before include "terrorist groups" , "Mobile phone in the US" , "Accommodation for prisoners" , "Rooms for prisoners" , "Basic structural units of all organisms" .)
'battery units?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tests that I've seen before include "Trials -- tribulations" , "International cricket matches" , "Trials for cricketers" , "Examinations, trials" , "Critically examines" .)