"Modern" Batteries, Alternator, & Voltage Regulator

[Gregory]

I think my Indy has gone over to the Dark Side.

I took mom's 2007 R320 CDI to the indy because the check engine light came on and it went into limp mode. Also, for the last couple months the oil level warning and the check coolant warning came up on the monitor. Both levels checked out just fine.

Indy calls back and says the batteries (starter and the Aux under the seat) are bad, which caused the alternator to go bad. The alternator tests with 15.8V output. Wants $1100 to fix it. He quoted $300 for a new alternator, then called back and said it was $450, then called back and said it was going to be $650. Estimate is now at $1450.

There doesn't seem to be a battery problem. The car starts perfectly normally, immediately, even in bitter cold weather.

Indy says the "modern" batteries fail differently than the old style, and when they do, the computer electronics are affected, and the alternator goes out.

I did research, the voltage regulator is on the alternator, its reasonably common for the VR to fail. Its a $70-$100 part.

I took the alternator to a local auto electrics shop and they quoted $150 to repair and test the alternator, including a new VR. The commutators are worn rough, he said they could be sanded smooth as the fix, plenty of copper meat left on them. They have it now, will be repaired in 24 hrs.

After the alternator BS story from Indy, I'm concerned the battery story is also BS and they are actually just fine.

Can anyone share what they know about batteries causing the alternator to fail, and causing the computer to throw odd codes?