Here are common signs to look out for when diagnosing a potentially failing car battery:

1. Slow engine crank during start-up.
2. Dim headlights and electrical issues.
3. Needing frequent jump-starts.
4. Battery warning light illuminated on the dashboard.
5. Swollen or bloated battery case.
6. Age of the battery (3 to 5 years).

If you experience any of these indicators, it’s advisable to have your battery tested by a professional to determine if a replacement is needed.