Sign of life — plus renewed energy (5)
I believe the answer is:
pulse
'sign of life' is the definition.
(a person's pulse)
'plus renewed energy' is the wordplay.
'renewed' is an anagram indicator.
'energy' becomes 'e' (physics symbol as in E=mc2).
'plus' is an anagram of 'puls'.
'puls'+'e'='PULSE'
(Other definitions for pulse that I've seen before include "Heart rhythm" , "Heart beat - peas, beans etc" , "Series of rhythmic beats" , "Musical rhythm" , "Edible seed from various pod plants" .)