Car batteries rarely fail without warning — the signs are just easy to miss until you're stuck in a parking lot turning the key with nothing happening.
A slow, labored engine crank is usually the first sign — the starter is working harder than it should because the battery can't deliver full current. Dim headlights or interior lights, especially when idling, point the same way.
A battery warning light on the dashboard should never be ignored, even if the car still starts fine that morning — it means the charging system has detected a problem. Corrosion around the terminals (a white or blue-green crust) restricts current flow and accelerates the battery's decline.
Most batteries last 3–5 years in normal use, less in extreme heat, which shortens battery life faster than cold ever does. If your battery is past that age and showing any of these signs, get it load-tested rather than waiting for a no-start morning.