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Demonic
Well-Known Member
Yes, I ran into this issue when testing different batteries. The digital gauge on the dash is not only different from the true voltage, but the difference is not consistent. I verified by putting a volt meter on the battery while the car is running and then also running a voltmeter connected to the cigarette lighter while driving and comparing it to the digital cluster gauge. I'm assuming either it calculates the voltage from an algorithm instead of giving the actual terminal voltage, or it may be a system to dummy the reading out so people aren't confused or worried seeing the true fluctuations and differences associated with the smart charging system.
JohnVallo
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Mine too acts erratic.
I was on a 700 mile trip a while back, and was watching all the gages along the way. The battery voltage kept dropping... Kind of scared me. It started out over 13.5v, kept dropping at every check, and was down to 12.1. Everything was operating OK, and the next day it was back up to almost 14v. I have never had any king of battery or electrical trouble, so I don't pay much attention to the fluctuating gage.
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Rubyred17
Well-Known Member
I think it charged at higher levels until the battery is fully charged afterwards. I was always told that continually starting a car with a weak battery is hard on the alternator because it has to work harder to charge the battery to an acceptable level
Demonic
Well-Known Member
Yes the fluctuation is because of the smart charging system. The car doesn't have a traditional alternator with a fixed output. The bcm uses an algorithm to tell the alternator what voltage to output.
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galaxy
Well-Known Member
And none of these readings are direct reading gauges. Obviously better than an idiot light of days gone by, but...they are all processed information based on what the ECU tells it to say.
I drove my car the other day. It was 28° outside (50° in the garage). I cranked the car up and let it idle juuuuuust long enough for the idle to settle down (maybe 2-3 min). I creeped up the road to the entrance of my neighborhood maybe 1/2 mile away never exceed 2k rpm. By the time I got to the main road, 10 quarts of oil was already at ~110°?!?!?! Yea right :-/
I drove my car the other day. It was 28° outside (50° in the garage). I cranked the car up and let it idle juuuuuust long enough for the idle to settle down (maybe 2-3 min). I creeped up the road to the entrance of my neighborhood maybe 1/2 mile away never exceed 2k rpm. By the time I got to the main road, 10 quarts of oil was already at ~110°?!?!?! Yea right :-/
Genxer
Well-Known Member
Just to add info to the thread, I recently had to replace a battery and afterward, noticed voltage fluctuation that was swingly wildly from 14ish back down to 12.1. Never noticed that before. It was going up and down constantly. Not long afterward one day, I started the car and after 10 seconds or so it just died. I thought "what the he**?" Tried to restart a couple of times and it finally did. After getting the car back home I took the cables back off (which BTW got meticulously cleaned on the battery change) I cleaned the posts on the new battery and made them nice and shiny. Also made sure to get the cables pushed all the way down. After putting things back together, the voltage did still vary but not with such wide swings back and forth. If this is indeed a smart charging system this makes sense to me. A bad connection would confuse anything trying to monitor the battery.
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