Common Causes of Battery Failure

Hot or cold, a harsh environment has a negative effect on automotive battery life. Slow cranking, especially during colder weather at this time of year, is often the first sign of a failing battery.
The battery has three functions as a major source of energy:
- Engine cranking
- Voltage stabilizer
- Alternate source of energy when electrical demand is high
When replacing a battery, the new battery should match the specifications of the original battery in order to maintain proper vehicle performance. (Fig. 2)

Fig. 2
Battery Ratings
A battery may have three ratings: amperage hours (AH), reserve capacity (RC), and cold cranking amperage (CCA).
The amperage hour rating is the maximum amperage discharge rate that allows the battery to maintain a terminal voltage of 10.5V at 80° F (27° C) for 20 hours. For example, a 100 AH battery should provide 5 amperes for 20 hours at 80° F (27° C).
Reserve capacity is the amount of time in minutes it takes a fully charged battery, being discharged at a constant rate of 25 amperes and a constant temperature of 80° F (27° C), to reach a terminal voltage of 10.5 volts
The cold cranking amperage is an indication of the ability of the battery to crank the engine at cold temperatures. The cold cranking amperage rating is the minimum amperage the battery must maintain for 30?seconds at 0° F (?18° C) while maintaining at least 7.2?V.
Electrolyte Freezing
A typical automotive battery is a flooded cell lead-acid battery. It is formed when two chemically dissimilar plates, divided by a separator, are placed in a solution called electrolyte. In typical automotive batteries, one plate is made of lead and the other of lead dioxide. The electrolyte is a solution of 64% water and 36% sulfuric acid. A chemical reaction occurs between the positive (Fig. 3, A) and negative (Fig. 3, B) plates and electrolyte solution (Fig. 3, C) that create approximately 2.1 volts of electrical energy. As a battery loses its charge, the chemical composition of the electrolyte changes and it becomes more like water.

Fig. 3
The freezing point of electrolyte depends on its specific gravity. A fully charged battery will not freeze until the ambient temperature gets below ?65° F (?54° C). However, a battery with a low state of charge may freeze at temperatures as high as 20° F (?7° C). Since freezing may ruin a battery, the battery should be protected against freezing by keeping it properly charged above 80?percent state of charge, where the freezing point of the battery will be somewhere below ?25° F (?32° C).
Common Causes of Malfunction
Regardless of the environment, 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, check for these common causes:
- Vehicle accessories left on after the ignition is turned off
- Regular short trips in stop-and-go traffic, and with many electrical accessories in use, such as the air conditioning, headlights, wipers, rear window defroster, etc., that do not allow enough time to properly charge the battery
- The electrical load has exceeded the generator output, particularly with the addition of aftermarket equipment
- Existing charging system conditions, such as a slipping belt or a generator that is not in proper working order
- The battery has not been properly maintained, including a loose battery hold down or missing battery insulator
- Electrical system conditions that draw down battery power
Parasitic Draw
Components most likely to cause a parasitic draw on a vehicle's battery are switches, relays and control modules. After the ignition is turned off, the control modules will begin to go to sleep (shut off). All control modules do not go to sleep at the same time; some may take up to 30 minutes or longer after turning off the ignition before going to sleep, like the Body Control Module (BCM). Others modules are designed to periodically wake up, perform a task, and go back to sleep at regular intervals, such as the OnStar and keyless entry control modules. These are all normal conditions.
For example, an engine off natural vacuum evaporative test can occur if the Engine Control Module (ECM) determines the drive cycle has met the appropriate criteria immediately after key off. The ECM will stay awake and the vent solenoid will stay energized for as long as 45 minutes. The typical current draw for this is about 1 A.
The remote keyless entry receiver also consumes an extremely low mA current for monitoring purposes. Actual system wake up only occurs when the key fobs for the vehicle are used. When other devices on the same remote keyless entry operating frequency are activated, the receiver will have a 100?mA spike. These spikes are normal and should not cause excessive battery draw.
Check any possible aftermarket equipment that may cause an unacceptable parasitic current drain. Aftermarket accessories installed into the courtesy lamp circuit can cause the inadvertent power timer in the BCM to keep resetting, which could cause the BCM to remain awake and cause a current drain on the battery.
Battery Testing using a Conductance Tester
Conductance is a measurement of a battery's current producing capability. This technology can help accurately identify batteries that have reduced performance after being in service. When using a conductance-type battery tester on side terminal and top stud batteries:
- Make sure the battery in the tester is not weak or inaccurate readings may result
- When testing side terminal or top stud batteries with a conductance tester, always use lead terminal adapters. Make sure the terminal adapter makes good contact with the lead pad of the battery or inaccurate readings will result
- Never use steel bolts when testing a side terminal battery with a conductance tester
- Never clamp the tester's leads directly to the studs when testing a top stud battery with a conductance tester
- ACDelco ST-1201 side terminal/top stud adapters are for the charging and load testing of batteries only. They should not be used when testing a side terminal or top stud battery with a conductance tester. Inaccurate readings will result due to the coating on the ST-1201 adapters
Conductance-type battery testers should never be used to determine state of health, state of charge, or CCA rating of a new, never installed battery. New batteries will develop their full performance capabilities only after a period of cycling in a vehicle.
To check the condition of a battery prior to installation, measure open circuit voltage (OCV). An OCV of 12.24V is adequate to provide the power requirements for starting most vehicles under most conditions.
All batteries will self-discharge and deteriorate in condition over time, which makes proper rotation and proper storage -- a battery stored at 95° F (35° C) will self-discharge twice as fast than one stored at 75° F (24° C) -- of inventory essential.
- Thanks to Todd Merkle








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