Energy finally picks up anyway (2,5)
I believe the answer is:
at least
'anyway' is the definition.
('at least' can be a synonym of 'anyway')
'energy finally picks up' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'finally' becomes 'atlast' ('at last' can be a synonym of 'finally').
'picks up' is an insertion indicator.
'e' going into 'atlast' is 'AT LEAST'.
(Other definitions for at least that I've seen before include "Eat salt (anag) - if nothing else" , "'If nothing else (2,5)'" , "As a minimum" , "Anyway" , "No less than" .)