Originally Posted by xfirepop

Hi All,

As an old time mechanic I learned that once an engine is running the battery is out of the running circuit. It is only being recharged once the engine is running. The electrical load is transferred to the alternator and the voltage regulator (now built into the alternator) steadies the voltage to the vehicle.
As we moved into the more sophisticated electronic systems the voltage to the computer became more critical. Therefore when the battery goes bonkers (sulfates and such) and the voltage it's drawing from the regulator is changing, the regulator is giving electrical surges or just not enough voltage into the once stable system. Depending on the amount of voltage spiking it will affect different systems through the computer.

We used to diagnose the battery vs alternator by simply removing the battery cable from the battery once the engine is running. If the engine continued to run the battery was bad if the engine died the alternator was bad (Yeah troubleshooting was much easier on my '70 SS 396). With todays electronics and delicate computers I don't recommend that, but the basic theory still applies.

The best test is a load test on a battery, not a voltage check. The voltage check does little to tell you the condition of the battery. A load test begins to tell you about the battery. You can go further to find out why the battery is bad, but if its bad...its bad. Replace it.

As a side note it isn't just Crossfires that have the problem. My daughter's Honda Hybrid was doing all kind of weird things and the dealer was going the wrong way with it. I had her replace the battery and guess what? Yup all the weirdness went away. I got a refund for their incompetence.

Sorry for the long dissertation. But I learned along time ago to not overlook the simple things and why they work, they can drive you nuts if you over think the situation. BTW electrical diagnosis was my speciality as a master ASE auto tech.

Rick