Electrical Systems of Today

thumbmaker.phpWe all dread that moment when we’re getting ready to go to work, get inside our vehicles, turn the key and…. click, tatatatata…..or silence….

Oh yes…should have replaced that battery! No problem. You find somebody to jump the car, drive to the nearest auto parts store and have somebody replace that battery for you. Problem fixed. Of course, this scenario is very general and doesn’t apply to any modern BMW of today. In fact, soon it will probably not apply to any car in the near future.

BMWs have always been at the forefront of technology. Over-engineered is an understatement when it comes to these cars. A late model BMW has such a complex power/charging system that one needs to have a degree in electrical engineering to be able to fully decipher. It all starts with the battery of course. Absorbent Glass Mat (AGM) batteries have been pretty standard in these and many European cars for their many benefits. Among the advantages of an AGM battery are:

  • Spill proof
  • Low maintenance
  • High current on demand
  • Cold weather performance


Performing an Energy Diagnosis Test with ISTA software

Performing an Energy Diagnosis Test with ISTA software

As durable as these batteries last, nothing lasts forever of course and when it’s time for replacement, this is when things start to get interesting. If we go back to the earlier scenario, steps must be taken before and after replacement of the battery to meet and follow the manufacturer’s original design criteria. If these steps aren’t followed, the vehicle will self-destruct! Ok, so maybe not. Just a little stretch of the imagination. What could potentially happen is a multitude of warning messages and electrical gremlins that may result. This can lead to unnecessary diagnostic time, to uncover a problem that shouldn’t have happened in the first place.




Over the course of a battery’s life span, many factors influence the way the vehicle’s charging system keeps the battery fully charged. All these factors are constantly been evaluated by various sensors and control units engineered into the vehicle. IBS or intelligent battery sensor keeps track of the battery’s state of charge, continuous measurement of current, and acid temperature, among other things. The various microprocessors in the vehicle take this information to calculate how the battery should be ultimately charged and influence vehicle electrical behavior. Lets say you accidentally leave a map light on. Theoretically, there should be a programming logic that is designed to shut that particular circuit, should the battery reach a certain level of charge. This is true as well when you have the radio running with the car off. After reaching a predetermined amount of time, you would get a message indicating it is time to shut off the tunes, or start the vehicle to avoid further battery depletion.

When a breakdown does occur, one needs to investigate and perform a systematic diagnosis of the source of the fault that will lead to a lasting solution to the problem. Energy Diagnosis is such a test. Built into the BMW diagnostic software, this test needs to be done BEFORE battery replacement to find out why that battery went down in the first place. The vehicle stores a “profile” of how the vehicle is driven over the course of 30 days. This can lead to the source of battery depletion. Did something “wake up” the car frequently, i.e. alarm system, lights switched on too long, faulty control unit? Was the vehicle driven for very short distances? Or did the battery just failed because it reached the end of its life span.





Once a diagnosis is obtained, a repair is made as necessary and the battery replaced, one final process needs to be performed AFTER replacement. The new battery needs to be “registered” to the vehicle. This effectively deletes the driving profile and a new profile is made to take into account the new battery. As such, if a battery is replaced and the vehicle doesn’t know this, that new battery will be treated differently. This is what will lead to those warning messages and a battery that won’t last a year. Furthermore, if a battery is replaced with that of a different capacity and/or different amps per hours, one must perform a battery “retrofit”. This achieved by means of programming to be able to let the vehicle know of the change.


So the method of actually replacing the battery is the same, it is the way this replacement is treated that has changed. This is one reason why we in this industry need to keep up with this changing technology. Lesson learned. BMW hides “Uncle Sam” inconspicuously in your vehicle to keep track of your electrical system.