Bet it's a battery (11)
I believe the answer is:
accumulator
I believe this is a double definition.
'bet' is the first definition.
(I've seen this before)
'a battery' is the second definition.
(accumulator is a kind of battery)
'it's' is the link.
(Other definitions for accumulator that I've seen before include "Electric cell; bet" , "Bet; large battery cell" , "one will be placed on a charge" , "Battery - type of bet" , "Person hoarding things