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.

•	An electrical short

•	A slipping belt

•	A bad generator

•	A bad generator voltage regulator

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

The freezing point of electrolyte depends on its specific gravity. A fully charged battery will not freeze until the ambient temperature gets below -54°C (-65°F). However, a battery with a low state of charge may freeze at temperatures as high as -7°C (20°F). Since freezing may ruin a battery, the battery should be protected against freezing by keeping it properly charged. As long as the green eye is visible in the hydrometer, the freezing point of the battery will be somewhere below -32°C (-25°F).