Boland01

After reading this string of comments I just hooked my digital charger to my car. It read 12.0 volts. The car has been sitting in my garage for 7 days now without being started. I did open the door and pop the hood before right before I hooked up the charger which may have given me a false reading due to the fact the car was no longer in sleep mode.

I'll be interested to see how this string progresses.

Boland01

After putting my battery on "trickle charge" for 75 minutes it's now reading a 100% on my charger. The charger automatically shuts off at this point. After waiting 30 seconds I hooked the charger back up and it now reads 13.3 volts. I'm assuming/hoping my battery is good.

TeRC_19kilo

My battery was beginning to give me starting problems, ie slow cranking or just wouldn't start. I charged it overnight outside of the car and took a reading, 12.79. I let it sit for about 2 days outside of the car and the reading was 12.60. At that time I had it tested at Autozone and they said it was still good. So I put it back in. Car started fine throughout the day, but at the end of the day it started but cranked slowly again. Any recommendations?

umermariner

Check Ur alternator...

BimmerFan52

Could still be the battery. After fully charging take it to an auto store to be load tested. Some batteries will read a full charge, but once loaded the voltage collapses immediately.

I don't think you said which kind of battery (FLA or AGM) you have, which if registered properly can affect the maximum system voltage designated by the ECM if the IBS sent info that the battery state of charge is low.

With a battery charged 80% or more, the normal system voltage set by the ECM (set by signaling the alternator to vary its current output which against the total system load will set the system voltage), will be in the range of about 14.1-14.3V.

But if the battery state of charge is low, the ECM can signal the alternator to bump up the system voltage to as high as 14.7V for black top AGM batteries, and up to 15.5V for FLA white top batteries.

After you start the car and give the alternator 15 seconds to increase the field current and ramp up, then measure the system voltage under the hood. Should be in the 14.0V - 14.7V for AGM or 14.0V to 15.5V for FLA.

If you are getting less than 13.7V then you can be pretty sure the voltage regulator on the alternator is gone. If you are getting more than 15.5V then you can be pretty sure the voltage regulator is on the way out.

However, sometimes a voltage regulator on the way out can be intermittent, acting correctly at one point in the drive, and then going off the deep end. When mine failed, at startup it would be 17V, then go to 11.5V then settle in just under 14V. I had to run a cigarette lighter voltage meter to follow the changes.

If the battery is good and the voltage regulator is good then the next thing to look at is a serious parasitic drain which is sucking the battery down in 8-10 hours. Common causes are an aftermarket device you added which stay on after the engine is turned off and the key removed, or maybe your IBS is bad (common on early E60s due to water damage).