Lester is running about, as always full of energy (8)

I believe the answer is:

tireless

I'm a little stuck... Click here to teach me more about this clue!

'full of energy' is the definition.
(I've seen this before)

'lester is running about' is the wordplay.
'running about' indicates anagramming the letters.
'lester'+'is'='lesteris'
'lesteris' is an anagram of 'TIRELESS'.

'as always' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.

Can you help me to learn more?

(Other definitions for tireless that I've seen before include "Never wearying" , "Full of energy" , "Having inexhaustible energy" , "Indefatigable, unflagging" , "Permanently lively" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.