One may have sunk eight pints, full of energy (7)
I believe the answer is:
galleon
'one may have sunk' is the definition.
(galleon is a type of ship)
'eight pints full of energy' is the wordplay.
'eight pints' becomes 'gallon' (I've seen this before).
'full of' means one lot of letters goes inside another.
'energy' becomes 'e' (physics symbol as in E=mc2).
'gallon' going around 'e' is 'GALLEON'.
(Other definitions for galleon that I've seen before include "Large old sailing vessel" , "Trader" , "Large old square-rigged sailing ship" , "Large Spanish sailing ship of yore" , "Old Spanish war-ship" .)