Did you hear a clicking noise?

Can you turn on the radio?

How did you test the battery?

Check to see if the battery cables are tight.

Try jumping it and if it still has no power then it sounds like the main relay.

It also could be that the alternator died on the way home and the battery was running the ignition.

I would take the battery in and have it checked. If it is good then look for loose wires. Then check the relays.