Top up (9)
I believe the answer is:
replenish
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">top up</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for replenish that I've seen before include "Restore" , "Restock, refill" , "Help siren (anag) - make up" , "Replace" , "Refill or make complete again" .)