There are a few signs of a dead battery to look for:
Your car doesn't start when turning on the ignition.
Your car starts but then dies right away.
The motor cranks but the engine won't start.
The engine takes longer to crank.
The "Check Engine" light is on.
Your door lights don't turn on, even though they're switched on.
Your headlights don't work.
Your battery looks damaged, corroded, or swollen.
You can smell rotten eggs from your battery.