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2008-2013 Cadillac CTS General Discussion Discussion, Battery Voltage Question in Cadillac CTS Second Generation Forum - 2008-2013; Originally Posted by Tbbt The voltages shown in the DIC without the engine running CANNOT be used for any diagnostic ...
  1. #16
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    Re: Battery Voltage Question

    Quote Originally Posted by Tbbt View Post
    The voltages shown in the DIC without the engine running CANNOT be used for any diagnostic purpose. They are blotto (scientific for stupid) and don't associate with any known fact!

    There is 'something' diverting some of the voltage away from the DIC. It's almost like there is a dead short (though I know that's not it) changing the voltage to 12.2v. I checked everything I could without tearing my car apart and can't figure it out! For instance, I drove my car doing errands, the DIC showing anywhere from 13.8v to 14.4v while in motion. I stopped the car turned the key to off, turned it back to the run position and the voltage returned to 12.2v.

    So while the DIC gives good engine operating voltage, the non engine running voltage is useless. If any one knows more, please feel to enlighten me. I'm stumped.

    Thanks, Marv
    Well Marv my friend, what voltage do you expect to read? 12.2 sounds good, mine was 11.7 earlier today. If you could look inside the battery you would find the missing voltage. As a battery ages the internal resistance increases and when current is drawn there is a voltage drop as a result of that resistance. Owm's Law E=IR.

    The static voltage of the battery (no current) will also drop based on the age and condition of the battery.

    As for the DIC, it is reporting with great accuracy (+/- .1 volts in my car), the voltage at the battery. The 14+ volts with engine running is the charging system voltage need to charge the battery and run all the stuff.

    You have been enlightened, do you feel any better?

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    Re: Battery Voltage Question

    Quote Originally Posted by Tbbt View Post
    So while the DIC gives good engine operating voltage, the non engine running voltage is useless. If any one knows more, please feel to enlighten me. I'm stumped.

    Thanks, Marv
    When I open the hatch on my 2013 wagon and put a voltmeter on the connected battery terminals, the reading is also 12.2 volts.

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    Re: Battery Voltage Question

    Same here, but why? Very odd! Same at the jump start location.

    Tomorrow I'm going to take my negative battery cable off and check the voltage. It won't be 12.2v when the negative is disconnected. It will be more like 12.6v.
    What will disconnecting the battery screw up?

    Marv

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    Re: Battery Voltage Question

    I turned the key to on in the garage. Lights come on, heat-ac off, radio off. DIC reads 12.0 volts. Power up the hatch to check the battery terminals and they read 12.19 volts. That would make me think the DIC reads about 0.2 volts lower than the battery voltage, and that the OP does not have to worry about his battery.

    I will guess that the fob antenna and security circuits add enough to interior lights to keep readings low. Of course, to test that, I need to disconnect the battery, and I'm not so sure I want to "throw" that code.

    added next day:
    I hadn't used my CTS for about 20 hours, and I checked battery voltage before I started the car. The DIC read 11.9 volts, which indicates about a 0.2 volt drop per day due to active clock, key fob, and security systems. IMO That's not too bad. When I started the car, the voltage reading rose to 14.8 volts in less than a minute as the alternator took over the readout.

  5. #20
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    Re: Battery Voltage Question

    A battery is a cheap investment. At this point it does not owe you anything. Change it while it is still convenient to do so. You don't want to be stuck and wish you changed it.

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    Re: Battery Voltage Question

    Quote Originally Posted by Joe View Post
    A battery is a cheap investment. At this point it does not owe you anything. Change it while it is still convenient to do so. You don't want to be stuck and wish you changed it.
    AAA

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    Re: Battery Voltage Question

    Speaking of replacement, are the factory batteries standard lead acid type or AGM?

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    Re: Battery Voltage Question

    The OEM batteries are lead acid wet cell not AGM. They must be 100% sealed and have the vent tube port to vent the gasses out of the trunk. You should be able to find a replacement for less than $130 vs >$230+ for an AGM battery.

    AGM is a very good technology for the right situation, but it is overkill for our cars IMHO. Very high priced and not necessary. With. the battery in the trunk, it doesn't see the high under hood temps that shorten battery life.

    I didn't have the opportunity to work on my CTS today, had some unexpected problems come up today (like 4" of rain) that diverted my attention. Hopefully tomorrow. I plan on hooking up my motorcycle maintainer to the jump start posts, then disconnect the negative battery cable and do some OCV checks and see if I can find the electronic 'sponge'.

    Marv

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    Re: Battery Voltage Question

    Quote Originally Posted by Tbbt View Post
    I plan on hooking up my motorcycle maintainer to the jump start posts, then disconnect the negative battery cable and do some OCV checks and see if I can find the electronic 'sponge'.

    Marv
    Don't forget to look inside the battery Looking forward to your findings.

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    Re: Battery Voltage Question

    Quote Originally Posted by Mistercoffee2 View Post
    Don't forget to look inside the battery Looking forward to your findings.
    Always hate to disagree with a friend, but it's not a low battery that is showing up here. A battery with an OCV of 12.2v is only 50% charged. With a working charging system, a fully charged battery would be in the 12.7 range. I do understand what you're saying about resistance, but this isn't what we are seeing in out CTS. I understand how batteries work and why they don't!

    This is something else built into the electrical system that magically reduces the voltage 'seen' in the system to 12.2v. I'll prove it tomorrow!

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    Re: Battery Voltage Question

    Quote Originally Posted by Tbbt View Post
    Always hate to disagree with a friend, but it's not a low battery that is showing up here. A battery with an OCV of 12.2v is only 50% charged. With a working charging system, a fully charged battery would be in the 12.7 range. I do understand what you're saying about resistance, but this isn't what we are seeing in out CTS. I understand how batteries work and why they don't!

    This is something else built into the electrical system that magically reduces the voltage 'seen' in the system to 12.2v. I'll prove it tomorrow!
    Compare it to my readings which I got yesterday. Nothing on, no trunk light: 12.05V, open circuit voltage: 12.29V. Certainly not fully charged. But that's all this battery will do in it's condition. Not bad for a 5.5 year old battery 8hrs after charging.

    So, I will go on a limb and say that your OCV will be .2V to .3V higher then what you see connected. And if you are getting 14.5V with the car running, as mine is, you have a a battery that will no longer charge to 100%. Or, maybe your car is a voltage sucker.

    Also, I would much rather disagree with a friend then an enemy.

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    Re: Battery Voltage Question

    OK folks, (all readings with engine off, unless noted)

    This AM my DIC reads 11.98v, Engine running DIC 14.6v, Battery OCV 12.22v, Under hood Jump Start location 12.20v. Removing the Neg. battery cable results in 12.66v OCV. So, I think there is something in the system that prevents full OCV from reaching the DIC w/engine off.

    As I stated previously, the DIC voltage cannot be used as a diagnosis of your battery condition. But it can show that your charging system is working.

    MrCoffee, If you charged your battery for 8 hours and it is still only maintaining 12.2v, then you are right, it's fading! Love your emoticons!

    As for my car, if my battery makes it through the winter OK, I'll replace the battery next spring with an AC Delco battery. It will then be 5 years old and working on borrowed time. The battery in my Ford Escape lasted 7 years (and still going strong when traded in), however it had removable vent caps for water addition (and associated acid corrosion maintenance). Sealed batteries do lose H2O, you just can't replace it!

    Does anyone here have schematics for the Battery Saver Circuit (also called Electric Power Management in the owners manual)? I would still like to understand why/how it works in our cars.

    The car alarm did go off when reconnecting the Neg. cable, but no other issues have surfaced!

    Marv

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    Re: Battery Voltage Question

    Quote Originally Posted by Tbbt View Post
    OK folks, (all readings with engine off, unless noted)

    This AM my DIC reads 11.98v, Engine running DIC 14.6v, Battery OCV 12.22v, Under hood Jump Start location 12.20v. Removing the Neg. battery cable results in 12.66v OCV. So, I think there is something in the system that prevents full OCV from reaching the DIC w/engine off.

    As I stated previously, the DIC voltage cannot be used as a diagnosis of your battery condition. But it can show that your charging system is working.

    MrCoffee, If you charged your battery for 8 hours and it is still only maintaining 12.2v, then you are right, it's fading! Love your emoticons!

    As for my car, if my battery makes it through the winter OK, I'll replace the battery next spring with an AC Delco battery. It will then be 5 years old and working on borrowed time. The battery in my Ford Escape lasted 7 years (and still going strong when traded in), however it had removable vent caps for water addition (and associated acid corrosion maintenance). Sealed batteries do lose H2O, you just can't replace it!

    Does anyone here have schematics for the Battery Saver Circuit (also called Electric Power Management in the owners manual)? I would still like to understand why/how it works in our cars.

    The car alarm did go off when reconnecting the Neg. cable, but no other issues have surfaced!

    Marv
    I hope this dies now.

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    Re: Battery Voltage Question

    I'll replace the battery next spring with an AC Delco battery.
    Marv[/QUOTE]

    are you guys of the opinion to stick with OEM batteries? It's probly not the
    most economical, but sometimes OEM pays you back. And you are right,
    most folks don't get a new battery until they're up against the wall. thanks, douglas

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    Re: Battery Voltage Question

    My preference would initially be for an AGM battery, for smell and corrosion protection.

    After that, I would look for a recent comparison test of various battery manufacturers.

    The last time I just bought an OEM replacement, the battery died in 2 weeks.

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