Common Causes of Battery Failure

After the battery has been charged or tested and has proven to be a good battery, the cause of the no-start or slow cranking condition must be determined to prevent comebacks. If no obvious cause is evident, the vehicles electrical system should be diagnosed using the following steps:

If the battery has passed a load test and the engine still will not turn over or is difficult to start, check the starting system. Refer to Starting System Check. System Check - Starting System
- If the starting system inspection reveals no abnormal conditions, but excessive cranking is required to start the vehicle, the cause must be diagnosed and corrected to reduce battery demands. Two possible causes for excessively long cranks are ignition system or fuel problems. Refer to Hard Start in Computers and Controls-3.1 L or Hard Start in Computers and Controls-3.8L.
- If the battery discharges while the vehicle sits for a few hours or days, the vehicle should be diagnosed for parasitic loads. Simple connection of an ammeter in series with the battery may not find the cause as the condition may not show up when power is restored unless that particular component is repeatedly cycled. Refer to Battery (Parasitic) Load Test Battery (Parasitic) Load Test
- If a battery becomes discharged and no excessive current drain is found, the operation of the charging system should be checked. Refer to Charging System Check.

Driver Related Conditions
If no cause is found for a discharged battery and the battery tests good, a light may have been left on or the driving habits of the owner may be such that, especially with many short trips and repeated starts, the generator does not have enough time to recharge the battery between starts.