Asche
wrecked
Colloquial for broken, destroyed, or unusable.
Nach dem Sturz vom Tisch war mein Handy komplett Asche.
After falling off the table, my phone was completely wrecked.

wrecked / exhausted
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wrecked
Colloquial for broken, destroyed, or unusable.
Nach dem Sturz vom Tisch war mein Handy komplett Asche.
After falling off the table, my phone was completely wrecked.

The adjective 'Asche' (wrecked / exhausted) comes from the noun 'die Asche' (ash). The figurative idea is that something has burned to ash — meaning it is completely destroyed or used up.
Die alte Festplatte ist leider Asche, alle Daten sind weg.
Unfortunately, the old hard drive is wrecked; all the data is gone.
This adjective is used almost exclusively predicatively, meaning after a verb like 'sein' (to be). Using it directly before a noun (attributively) is unusual.
Ich glaube, der Toaster ist Asche.
I think the toaster is wrecked.
'Asche' (wrecked / exhausted) in this use clearly belongs to colloquial language. It should be avoided in formal or written contexts.
Boah, ich bin so was von Asche, ich geh direkt ins Bett.
Man, I am so completely exhausted; I'm going straight to bed.
The exact meaning depends on the subject. If 'Asche' (wrecked / exhausted) refers to a person, it means 'exhausted'. If it refers to an object, it means 'broken'.
Nach dem Marathon war der Läufer komplett Asche.
After the marathon, the runner was completely exhausted.
finished / ready
'fertig' and 'die Asche' can both colloquially express that someone is very tired or exhausted. 'fertig' is much more general for this and is understandable in many situations. 'Asche' is very informal and sounds more like colloquial language used in certain groups. In addition, 'Asche' can also mean 'broken' or 'unusable', so context can be important. The words can be confused because both can describe a state of having no energy. 'fertig' is safer if you want to say neutrally that you are exhausted.

Nach der Nachtschicht war sie komplett asche.
After the night shift, she was completely wiped out.
Nach drei Stunden Training war Max richtig fertig.
After three hours of training, Max was really exhausted.