If the SOC measurement indicates a discharged battery, you'll need to identify the reason for the discharge. Today's charging systems are designed to maintain the battery properly and the only reasons for a battery to be discharged are age, faults in the vehicle's charging or electronic systems or extended periods of storage where the vehicle is not being used.
According to EnerSys, "When a vehicle sits for long periods of time, it can destroy the battery through repetitive deep discharges. Alternators are not deep-cycle chargers; their output is limited in operation. Elevated temperature can accelerate self-discharge and add to the total rate of storage discharge."
This high alternator demand can also cause damage to the alternator itself over time and it should never be relied upon to replenish a discharged battery. If your customer stores his/her vehicle for extended periods of time, recommend the use of a home battery maintainer to protect the battery and alternator from harm and premature failure.
In addition to the effects of extended storage, EnerSys shares, "Many times issues with a vehicle’s electrical system are automatically blamed on the battery. It is true that changing the battery is the easiest thing to do to start diagnosing an electrical problem, but that may not be the actual source of the problem. An example is when a parasitic load is causing battery and/or starting problems. Replacing the battery will only mask the problem temporarily. Taking the time to see why a vehicle may have trouble starting, or why a battery is constantly failing is key."
Better yet, make sure the battery has indeed failed prior to replacement - especially if it’s one that is not that old! This may require the battery to be charged and retested. Just remember what the experts have told us, though, and let the battery acclimate to room temperature and "rest" for a minimum of 10-12 hours. If the "rested" OCV is still below 12.4, replace it with confidence.
And young or old battery, be sure to test the vehicle's charging system to insure the new battery has a shot at a long and happy life!
Don't forget the reset!
According to industry sources, there are over 9 million vehicles in the U.S. fleet that currently require some form of battery "reset" or "registration" when replacing the vehicle's battery.
"Not performing battery reset functions can cause some vehicles to go into a weak battery mode that will affect the operation of non-critical electrical loads. This mode can be manually reset after replacing the battery via a tool connected to the OBD2 port. Not performing battery registration functions may result in short battery life. Some vehicles manage batteries differently as they age. They will also treat AGM and flooded batteries differently", says Knauer.
Bosch spells it out for us, by offering these notes, "Most stop/start vehicles will require an ECM update when a battery is replaced, to ensure the system works properly and the battery is being charged correctly. This includes newer vehicles from BMW, Mini and the Ford F-150, among others. The most important thing for techs to know or understand is that if they are replacing the battery on a start/stop vehicle, they should look for a battery reset procedure in their scan tool, or invest in a separate battery reset tool that is updated for newer model year vehicles."
They also shared some OEM specifics for the benefit of Motor Age readers:
Audi: many models require a battery information or battery replacement procedure, including popular models like the A6, A4 and many Quattro-equipped vehicles.
BMW: Most newer 1, 2, 3, 4, 5, 6 and 7 series vehicles require a Battery Exchange Register procedure to ensure a new battery is charging properly. Many BMW SUVs and Mini Coopers require this procedure as well.
Ford: The Battery Monitor System Reset procedure must be performed on many high-selling Ford models, including newer models like the F-150, Escape, Explorer, Fusion, Mustang, Taurus and many Lincoln models.
General Motors: Some Buick, Cadillac, Chevrolet and even Saturn models require a Battery Sensor Module Relearn or Battery End of Life Estimate Reset procedure.
Jaguar/Land Rover: Most 2009 – 2015 models require a Battery Replacement procedure be performed to protect a new battery from being overcharged.
Toyota: Most Toyota and Lexus models since as early as 2004 require a Battery Current Sensor Initialization procedure be performed after a battery replacement.
Volkswagen: The company’s most popular vehicles require a Battery Replacement of Battery Information/Replacement procedure post-battery replacement, some as early as model year 2000.
Volvo: 21 Volvo models and counting require either a Battery Replacement or Battery Replacement Second Battery procedure be completed to ensure expected battery life.
Other valuable tips
Our experts provided more information than I can fit in just one article. But there are still a few great tips and observations I think we need to squeeze in.