Liquid or gel in a battery (11)
I believe the answer is:
electrolyte
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">liquid or gel in a battery</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for electrolyte that I've seen before include "conductor" , "Liquid or gel containing ions - EEC telly rot (anag)" , "Fluid in a battery" , "Liquid or gel in a battery" .)