Coating, one in battery? (5)
I believe the answer is:
layer
'coating' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for layer that I've seen before include "See 22" , "Bed - hen" , "Lamina" , "Stratum; chicken" , "Single thickness and hen" .)