What must be paid to service the battery (6)
I believe the answer is:
charge
'service the battery' is the definition.
'charge' can be an answer for 'service' (thesaurus). I am not certain of the 'the battery' bit.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for charge that I've seen before include "Legal accusation" , "Accuse - rush - request payment" , "The price asked for goods or services" , "Accumulation of electricity" , "How much" .)