The most common and most likely answer to this crossword clue is the 5 letter word SAPPY
S
A
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More clues leading to the result SAPPY
Buddy explains!

The straight part
We know that "full of energy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case full of energy = sappy.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SAPPY mean?
SAPPY adjective- Excessively sweet, emotional, nostalgic; cheesy; mushy. (British equivalent: soppy)
- Having (a particularly large amount of) sap.
- Juicy.
- (of wood) Spongy; Having spaces in which large quantities of sap can flow.
- Musty; tainted; rancid.