Ronnie

What's your battery voltage after charging or driving for a while?

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Yesterday I thought I would put my Reatta's battery on the charger since it has been cool in the garage. It's down to about 46 degrees in there. After charging overnight with a 10 amp charger the voltage only reads 11.7 volts. This is a new battery that I got about a month ago. I thought the old battery I had would read about 12.3 volts when fully charged. Is my memory bad or did I get a bad battery this time?

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Posted (edited)

I checked my wife's battery on her Buick Enclave today [as we have been having starting issues due to the cold] and hers read 11.9 voltss. I put it on a charger so I could check it again to see what we get. The alternator was putting out 14.4 volts so that is good.

Edited by DAVES89 (see edit history)

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Do you mean volts Dave? No need to get out in the cold to check it. Thanks! I will take the battery back to NAPA next week and let them check it to make sure it's OK

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My battery is typically 12.6-12.7 volts after sitting in the cold garage all night. Maybe 12.5 if I don't drive it for a couple days. If I run it low while working on something I put my 8 amp charger on all night. It starts out at about 6 amps and tapers off to about 1 or 2 amps. The voltage still ends up at about 12.6. If your battery only comes up to 11.7 then you may have an issue.

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That's way off if just off the charger. What's the voltage while charging? Usually around 12.8v  fully charged after the excess surface charge from a fresh charge burns off. Normal charging voltage should be 1.0v-2.0v above nominal battery voltage as it nears full charge. Voltage will be low if the battery is pulling a lot of amps while charging. I would bet the new battery has a dead cell.

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A fully charged battery should read 12.6 a good charging system should show somewhere between 13.8 to 14.5 the best way to see how good a battery is is to load test it by putting a load on it of 250 amps for 30 seconds and it should not drop below 9 volts stop the test wait 30 seconds to allow the surface charge to come back and perform the load test again  it should still hold 9 volts. Food for thought, When you start your car it takes around 7 miles to warm the car up then it takes another 7 miles to charge the battery ( doing this you could get 7 years out of a battery) and burn off all the hydrocarbons out of the engine and exhaust. In other words everytime you start the car you should drive it 14 miles which most people don't do. That is the reason for a lot of the problems that accur.

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Thanks for the help guys. I thought 11.7 volts was low. I'm going to put the charger on it tonight and leave it on until morning. I'll check the voltage while it's charging. I think the battery has a problem but it might be a problem with my old charger.

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This turned out to be an easy fix. The lead on my old multi-meter is making a bad connection. I got out my new meter and the voltage read 12.4 volts without putting the charger on the battery. Problem solved. Thanks for your replies!

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In these cold months mine reads right at 14.0 volts. I actually just put a new battery in it.. But the old battery (which by the way, the date sticker read 11/09!!!!) That was crazy to see that the Reatta had such an old burnt out battery in it. But I noticed a few things when I put a new battery in, The CRT doesn't gitter and fade anymore, the headlights pop up everytime, and the dash and headlights are much brighter. With my old battery I didn't see a voltage above 12 volts, and the car took 1 or 2 times to crank up, and the driver headlight never popped up ( I had to do it manually) So I guess always make sure you have a healthy battery in there, especially in these cold cold months!

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If you have a battery that has 14 volts without the engine running you have an exceptional battery. I've never had one that would read over 12.5 fully charged. If I look at the gauges on my car with the engine running the charging voltage varies but it's usually around 13.9 volts. I guess the battery fully charged voltage varies by battery and the charging system. My engine hardly turns at all before it starts and I guess that is what really matters.

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Posted (edited)
11 hours ago, Ronnie said:

Do you mean volts Dave? No need to get out in the cold to check it. Thanks! I will take the battery back to NAPA next week and let them check it to make sure it's OK

Thanks Ronnie, I made the correction. This series of post is interesting as I am having issues with my wife's Buick Enclave. I bought it at a local chain store and when I installed it I found the positive post was a bit smaller then what the new style clamp would tighten down to. I mentioned that to a friend of mine and he suggested installing a shim, which he made by  slicing up a soda can. The problem persisted so I took the battery out and they tested it which took several hours. 

 I will note that this is not the correct battery for the car but the guy who assisted me gave me one that was a bit more powerful then the recomended one. It was correct in all the physical dimensions, but could the post be a different size?

 So with this cold snap we have been having starting problems that require "help" using a 50 amp charger for 10 minutes or so. Then it starts. I caught up with my friend yesterday and this time we used a small copper strip to replace that aluminum can strip to give us better condectivity. The battery at the time was 11.9 volts and when we started the car the alternator was putting out 14.4 volts.

 The Enclave is always kept in an unheated garage and the temperature right now is -7 degrees so I am going out now to give it a start. If it starts great then I think the copper strip made the difference. If it doesn't I am taking it the car in to show the store service writer what we did and what we have experienced.

 I really think we have a dead cell, but they say not.  

 Maybe that strip has made the difference as the car just started. We will continue to monitor this. 

Edited by DAVES89 (see edit history)

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Dave, I don't know if you can do this on newer cars but here is a trick old mechanics would use to determine if a battery has a bad cell. I still do it if the battery has caps that can be removed.

 

When the battery will not turn the engine or turns it really slow do the following:

First remove the caps from the battery so you can see the water in the battery.

Then have someone hold the key to the start position and hold it there while you look at the water in the battery (Best to wear a face shield or safety glasses)

If you see one cell that looks like it is boiling, that is a bad cell

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The battery is a sealed battery. I just turned the car off and will try starting it later this morning. We are dealing with exceptional cold weather [yes even for Wisconsin] and this is a good test. However it also looks like the cold snap we are experiencing is finally going to move east and we will be warming up. 

 I am encouraged that the car started right up after sitting for about 15 hours in sub zeroi weather. Like I said we will monitor it if it persists I will make an appointment to take the car in and let them tell me what is going on. The store chain is a regional one and is known for good service with good quality items at a fair price [FleetFarm] that 2sater is very familiar with.

 So far no one has gotten starnded and there is only a minor imconvienance with the first start in the morning.

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Dave, you should check to make sure the bolt that holds the cable isn't bottoming out in the threaded hole in the battery before the cable is tightly clamped to the battery. Remember the problem I had with that a few years ago on my Reatta? I was almost stranded away from home because of it.  Battery Cable Checks & Repair

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Posted (edited)

Sorry Ronnie, I have been talking about my wife's car a Buick Enclave. The Black has started great all through this cold snap.

Edited by DAVES89 (see edit history)

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I was assuming it had a side post battery but I'll bet it's like my Equinox and has a top post battery. My bad.

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Yep top post in front of the passenger middle seat under the floor. Have to remove the floor mat, 2 vinyl floor trim pieces and one carpeted panel. Easy 10 minute access especially in sub zero weather.

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At least they kept my Equinox battery under the hood. It's kind of hidden under some stuff but it does have a remote battery post for jumping it off or charging the battery.

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14 hours ago, retired mechanic74 said:

A fully charged battery should read 12.6 a good charging system should show somewhere between 13.8 to 14.5.

I agree that any good functioning charge system should put out a minimum of 13.8 volts but....  (and this is going from memory of working on Fords back in the sixties and seventies) I always thought the range was 13.8 to 15.2 with an average of 14.5 being what you wanted to shoot for.  Are you saying you shouldn't see over 14.5 volts on a good charging system?

I have seen cars at 14.9 - 15.0 right after startup and then after a few minutes settle down in the 14.5-14.7 range. I have advised people who questioned when it's over 12 volts "no the system is not overcharging and no fear of "boiling" the battery". Should I be rethinking what I have practiced for 50 years? I only ask because I know you are a retired  trained mechanic who has shared some very knowledgeable information. I have not been trained in this field but for over 50 tears have played with and worked on many cars & motorcycles.

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Mid 14's is normal voltage with a good strong alternator. A marginal alternator  (usually a failing regulator) will output lower - sometimes under 12 volts - and fail to apply a decent charge. I get about 14.3-14.8 volts on my 88's per the CRT gauge screen. Nominal voltage for automotive electrical systems is 13.8v, and most dedicated "12 volt" power supplies used to power automotive electronics outside a vehicle setting are setup for 13.8 volts DC regulated output.

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I think my alternator might charge more than 13.9 volts if I was driving it. That was what is was charging just idling in the garage. As soon as the weather warms up so I can drive it some I will check it again. Thanks everyone for your comments.

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Ronnie, keep in mind that the alternator has an internal voltage regulator. This should maintain a voltage range of between 12.5 min and 15 volts max output when the engine is running, irrespective of engine speed and load on the electrical system. Voltage will tend to increase with engine speed - and decrease under heavy loading - but should remain range bound as above for everything to function properly and not be into under/overvoltage conditions.

 

As well, the maximum available current output (measured in amps) will increase with the engine speed. The stock alternator on a Reatta is a 120A version of a CS140 large body GM alternator. The full 120 amps will not be available at idle (approximately 600 RPM at warm engine). The full rated output is usually available  at somewere over 2000 RPM. Larger output versions of this alternator are available, up to 300A with upgrades to the stator,  rotor and regulator.  These are usually custom built.

 

Getting this sort of ampacity from the alternator requires upgrading the cabling between the alternator and battery as well. Note too that the greater the max output is, the more current will be available at idle. I replaced one of mine with a 250A alternator to run a large 120 volt inverter (2500 watts) for emergency site power on occasion. Works well and doesn't nick the battery at high output demand from the inverter. Existing units can be rebuilt with such upgrades if you are so inclined.

 

 

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Kevin, Thanks for the information. I think alternator is probably working correctly. I rebuilt it myself about eight years ago. I know it got new bearings, brushes and probably a rectifier but I dodn't remember that for sure. Although it has been eight years ago it has only been about 20,000 miles ago. What made me suspect something was was wrong was when I routinely charged the battery overnight and just measured 12.7 volts the next morning. This is a new battery that has just been in the car for a little over a month and I panicked thinking I had gotten a bad battery that wouldn't fully charge. Turns out the problems was the leads on my old meter I was using. The leads have interchangeable probes that crew into the end the lead. They have gotten worn over the years and will not stay tight and make a solid connection. When I used my new meter with good leads the problem went away. I need to throw away the old meter. It's about 40 years old and isn't with buying new leads for it..

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There are static charges which are in the 12.3-12.6v range fully charged, and then there are surface charges (can be over 13v when just off charger but will bleed down in an hour or so). My cars most run about 14.1v when running.

 

Any battery that is under the passenger seat in a modern car is going to be an AGM (no outgassing). Whenever I replace a battery (except for the GC2s in my travel trailer) it is with an AGM.

 

A good battery that has been discharged will take a minute or two of charging for the voltage to come up. A battery that almost immediately goes from under 12v to over 14v is probably bad or failing.

 

I use one of these for evaluation but a $20 100A load tester can tell you about the same just with a needle.

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We have a new Harbor Freight store that just came to town. I would like to have a load tester for a battery. I'll see what they have in stock. I'm always looking for a good excuse to go there and look around. :)

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