Hi, I received this error message last week. I replaced the battery three years ago so naturally I thought it was the alternator. However, when I replaced it I still have the same issue. With the AC on, radio or operating the hood the voltage will go down and the car will go into Fail Safe Mode. It says the Battery is Not Charging. It is not throwing any codes. Could there be a bad cell in the battery or an issue with the electrical charging system? I put a volt meter on the battery. At rest it was 12.27 V. While running at idle the voltage is steady at 11.89. When a load is applied such as the AC it will go down and the guage on the dash will show that it goes below 9V.

 

Open circuit voltage for a good battery is 12.3 - 12.4 volts. Charging voltage at the battery should be between 13.8 and 14.2 volts. You'll need a DVOM to do voltage drop tests from the alternator back to the battery, with the engine running. I suspect you have a high resistance connection some where. Look for a voltage drop of more than 0.1 volt per connection.
Good luck,

 

I replaced the alternator but still have the same issue. I just had the battery loaded tested and everything is fine with that. There must be something in the charging system. Has anyone had this issue before? Is there something simple I can check first such as diodes or fuses? If not, I have to bring it to shop to get them to test from the alternator to the battery. Thanks.

 

Check fuse number 2 in the engine compartment fusebox (US/Canada driver side).

Check the heavy mains power connections at the starter and alternator for corrosion or looseness.

The the heavy mains power connections to three megafuses, and the megafuses themselves in the trunk behind the spare tire.