Did they ever have power? Relics, like people, do not have power. The power comes from God. If you have faith that God can heal, He will reward your faith.
And the Lord said unto Moses, Make thee a fiery serpent, and set it
upon a pole: and it shall come to pass, that every one that is bitten,
when he looketh upon it, shall live.
And Moses made a serpent of brass, and put it upon a pole, and it came
to pass, that if a serpent had bitten any man, when he beheld the
serpent of brass, he lived.
In the middle of the desert, people began to doubt God and speak against Him and His servant Moses. And so, God retired His divine protection from them, giving open way for the beasts of the desert to attack. Then God gave Moses the command to make a serpent. Was there anything special about the handcrafted serpent? No. Was there any power in it? No. Why have them look at it then? Because those who believed (had faith) in God and in the words of His servant Moses looked, and were healed by God. Those who did not and looked for their own remedy died.
The power is not in the relic. The power is not even in a person. The power comes from God Himself.