A battery is not designed to last forever. With proper care, however, the battery will provide years of good service. If the battery tests good but still fails to perform well, the following are some of the more common causes:

1. A vehicle accessory was left on overnight.
2. The driving speeds have been slow with frequent stops (stop-and-go driving) with many electrical accessories in use, particularly air conditioning, headlights, wipers, heated rear window, cellular telephone, etc.
3. The electrical load has exceeded the generator output (particularly with the addition of aftermarket equipment).
4. Existing conditions in the charging system, including the following possibilities.

•	A slipping belt

•	A bad generator

5. The battery has not been properly maintained, including a loose battery hold down or missing battery insulator if used.
6. There are mechanical conditions in the electrical system, such as a short or a pinched wire, attributing to power failure. Refer toGeneral Electrical Diagnosis Procedures in Wiring Systems.