@ActRaiserTheReturned Be creative, it is up to you. I and OP came up with our relics on a mythological/cultural basis and both took a bit of liberty with them, you can make the same with the stones. Zeus is not really a good of electricity, he is more of a King/Judge. The Stones represented divine or regal bloodlines, so perhaps they could also give your char some sort of ability in that sector. Than again you could also go with a more sky focused ability since they were carried by Zeus divine eagles.
Another idea if you want to go with electricity would be a weapon infused with it. A birthright could also be modern so a magical gun that shoots lightning is not out of the question. It could be forged by Hephaestus out of Adamantine and imbued with Zeus divine lightning. All this are just suggestions however, create what you feel is right but be creative.
Also I have a question. You have written that your char is not good at sports yet he has athletics and was somehow able to defeat a whole gang of thugs?
Also I realize I sound a bit hostile but again, not my intention.
@Avanhelsing Sorry if I take to much of a liberty here, you are OP after all
He was able to beat the whole group of gang members because before he was infused with Zeus'es lightning he was just a good looking guy, now he's empowered by Zeus.