2010 - Sudden 12V Battery Failure

Well now I see what part of the problem with dealers service departments IS.
That's a bunch of crap.

11 V is NOT in any way "standard voltage".
The chart says "discharged".

From reports here, anything below 12 might start showing problems.
And no battery I've ever seen reads 14 when the car is not running.
Whoever wrote that passage knows nothing about 12 V automotive batteries and it appears that service departments are following it blindly.

P.S. A wet cell battery does not have to be sulfated to self discharge. It's a chemical reaction thing.
They all do it even when brand new; AGMs a LOT less though.

 

Either that or they charged a new battery and left it for a very long time in a partially-charged state.

 

They are citing voltage measured when connected to the car. The chart is open terminal voltages. Apples and oranges.

 

The computers will probably be fine down to 11V. But a one-time measurement can't really tell you the whole story; many of the problems probably occur due to increased internal resistance in the battery, which causes the voltage to drop very low upon a heavy drain, and then rebound once the drain lessens. A momentary drop like this could easily cause a fault in a computer somewhere while still allowing it to power on.

Being more from the consumer electronics industry, I'd expect the computers to have some sort of power management hardware - it should sense that the supply voltage is below the allowable spec and reset the computer to avoid unintended operation. But maybe in cars, they aren't quite so aggressive about doing that so as to not accidentally reset the ECU due to some brief noise on the power supply?

 

Not being from the electronics industry, this is what puzzles me: Why are we using what appears to be 30-40 year old technology? Why are settings in volatile RAM lost when power is interrupted?

I'm sure there's a reasonable answer somewhere, but then again, maybe there isn't.

 

Some info here, worth bookmarking:

Diagnosing A Car Battery That Runs Down

There's a link on the above (electronic battery tester...) also with good info, maybe more links.

 

It is not "apples and oranges" .
If everything in the car is OFF, the readings should be exactly the same.
If the TINY little parasitic drain from the standby electronics makes a measurable difference in the battery voltage, then it is definitely getting weak.

 

Yes. Your battery probably is on the way out.
IF everything really was off overnight.
I think you should repeat the test again when the weather is warmer.
And if you have a battery tender, a good full charge might be in order too.

How did you access the battery in the morning to make the measurement ?
If you opened the door to pop the hood that reading probably was NOT with no load and it might be OK.

 

My thought: Why?

I mean why obsess over the condition of the battery as long as it's doing it's job? And despite much controversy in here, it doesn't have much of a job to do, other than booting up the computer and running accessories when the system is shut down.

 

Excellent find.
Mods/Admins: Any chance that these tables could be put into a sticky somewhere.......and/or posted so that they are visible without downloading ??

 

Our battery, which measured 12.42~44 volt just yesterday, was up to 12.75 after a modest drive today. Suspect if it sits a day or two it's gonna slump back down. Seems like driving amounts to a mild charge session, but it's not sustainable.

Yeah JD, that doesn't sound that good for brand new battery. Sounds like ours, lol.

 

JD,

I just measured the voltage of my one year old Optima Prius replacement battery at 12.72 volts in my 40 degree F. garage, about 7.5 hours after a 50 mile roundtrip.

Also, below is a link to an Optima User Guide. It has data on charging and troubleshooting that may be helpful. See troubleshooting test #2 where you test the battery's ability to hold a charge.

Good Luck.

http://d26maze4pb6to3.cloudfront.net/optimabatteries/1213/4333/7097/Battery_User_Guide.pdf

 

New or not, that reading is NOT good.
Did you fully charge the new battery before use ?? That can be important.
I wonder how much current your voltmeter draws; that shouldn't be a factor though.

Something is not right here. You may have one of those rare cases of excessive "phantom" drain while the system is off.

 

I am very impressed with the BatteryMINDer 2012-AGM. You can be assured that it will properly charge your AGM battery up to 100% SOC, then you can do reliable testing. Meaningful battery testing first requires that the battery be fully charged.

Again, best of luck.