Battery and alternator problems

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This has to be the mother of all coincidences. This morning my truck was just a little slow and hesitant to start. It had an Auto Craft Silver made by Johnson Controls battery in it, date of manufacture on it was November 2007. The truck did start though and I had to get to work and had no problems getting there, a 26 mile trip mostly on the turnpike. I went out to the parking lot on my last break around 3:30 and checked the battery voltage without the engine running, it was 10.5 volts. I used my trusty little cheapie $2.99 meter from Harbor Freight that is part of the tool kit I carry in my truck. I instantly thought it must have a dead cell. It was even slower than this morning but it did start in the parking lot and I let it run for a few minutes till I had to get back to my desk.

Now the odd coincidence is about 11:00 this morning my girlfriend calls me and says her car was also slow to start this morning but it did start and she drove it to work 4 miles from our house. She drove it across the parking lot to the grocery store to get change and a few things for the store where she works and her car would not start when she went to drive back over to her store. Her car had a Sears DieHard, I have no way to know how old it was and she does not know how old it was either. Her car, a 2003 Accord EX was always a little slow to start, but never had a dead battery until today. Her old battery had to have been at least 5 years old though.

I stopped at Autozone on my way home and got a new Duralast Gold battery for my truck. They don't stock my battery in the red top Duralast, and it was only another ten bucks anyway. I put in my new battery there in the parking lot and went to my gf's store, and checked her battery with my trusty Cen-Tech Chinese made meter, it had 12.5 volts with the engine off but still would not start the car. I jump started her car and off we went to the Autozone here in town. She bought a Duralast Gold for her car, I installed it in the parking lot and all is fine now.

Other than both batteries failing on the same day, the odd thing is this: At home I checked her new battery's voltage with my Fluke meter, with the engine off, it has 12.97 volts, engine running with no high beams and no AC running, it has 14.27 volts, and with the engine, AC and high beams all on, it has 14.0 volts at the battery terminals. This tells me her alternator and charging system are working fine.

On the new Duralast Gold battery in my truck, with my engine off I have 12.65 volts. Engine on with the AC and high beams off, I get 13.6 volts, and with the high beams, AC and radio on I get 13.6 volts then too.

The way I learned it is if your alternator is OK you should have about 14.2 volts with the engine running and the same voltage, right about 14.0 to 14.25 volts with the engine idling and the high beams and AC turned on.

I think her car is doing fine, but I wonder if I should replace my alternator. I drive a Dodge Dakota, 56 miles round trip to work 5 days a week and Dakota's are very sensitive to low or fluctuating voltage. I am really surprised and grateful that I had no problems driving today with a bad battery.

What do you guys think? Is 13.6 volts good enough or should I just replace my alternator now before it fails on me too? My truck is a 2001 Dodge Dakota, 3.9 liter V6 and it's the original alternator, has 134,900 miles on it and is 10 years old now according to the build date on the door jamb sticker.

Any ideas are appreciated here. Thanks.
 
13.6 is a bit low. switch your dvm to ACV and look for any AC component in the alternator voltage. That ac voltage should be very low-Just 20 milivolts or so.
 
I don't feel bad at all to change out the not so pristine 135k miles 10 years old alternator, you got your money out of the OEM alternator.
 
Thanks for the replies. There are 3 ground cables from the battery that I can see without taking anything apart. There's one at the engine block, it's on a bolt that is part of the bracketry that holds the power steering pump to the engine block. Then another from the battery negative terminal where it is bolted to a stud on the inside of the left front fender, and there are about 8 or 10 smaller gauge ground wires attached there too, I guess that is how Dodge connected some of the smaller ground wires running through the truck to the ground from the battery. And there is another heavy gauge ground wire bolted to the frame in the left front wheel well. All of the connections look good to me, they have no corrosion or anything that I can see.

The one in the fender well has been loosened and put back together, there are marks on the nut holding it together. I can tell the others have never been loosened at all. Other than being a little dusty and dirty they look solid and I think they should be OK. Tomorrow I will unbolt each one and hit them with a wire brush and solvent and clean them up and then test the battery and alternator voltage again. If I still have lower than normal voltage after that I will replace the alternator.

I was considering the Duralast reman alternator, $129.00 at Autozone. I have used Duralast chassis and brake parts with no problems, and I know the Duralast batteries are very good quality. Does anyone know about the quality on the Duralast reman alternator? I would think it would be a pretty reliable part, it is rebuilt by Nippondenso, and they are the OEM supplier for Dodge alternators. An OEM alternator from Dodge is out of my budget, I know they will run probably $225 to $250 or so, because a new alternator from Napa is $170.00 plus a core charge. Just to cover my bases I will check with Dodge tomorrow, but I expect them to be pretty expensive.

Thanks for the help here.
 
Google "battery voltage alternator normal"

Some of the information that comes up is about the battery and normal voltage, and some is about the alternator.

Anyhoo , one site said 13.5 to 14.4 is the normal range for the alternator voltage with a running engine.

Also some alternators will reduce the voltage when the engine compartment is hot. This is to reduce the battery fluid loss on hot days.

13.6 is within normal range. Especially in Florida in September.

If the ambient air temperature was 0F and the engine compartment were still not warmed up, then 13.6 MIGHT be considered pushing it for the low end of acceptable.
 
BTW, with that many miles I would replace the brushes and bearings on the alternator, and replace the brushes and bendix on the starter. Also check the serpentine belt and always replace the tensioner and idler puley when you change a serpentine belt. If you do the starter be sure to clean down into the little groves between the copper sections that the brushes ride on. Also be sure to put a very small amount of grease on the shaft ends and where the bendix rides.

If you do this work yourself you will save money and end up with a more reliable vehicle. Many re-manufactured parts such as alternators and starters are done by unskilled laborers and the quality is really bad.
 
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It is always a great idea to clean BOTH ends of ALL cables AND where they seat - nice and shiny.
If it doesn't fix a problem it will prevent one, and keep the system at peak efficiency.
Take 1/2 hour and do this, no matter what.
 
Thanks for the info Jim, but rebuilding the starter and alternator are beyond my scope.

I stopped by AZ on the way home tonight and they checked my battery and alternator with a hand-held digital load tester. Battery read the same 13.6 volts with the engine running and the load tester said the diodes and other innards in the alternator and the alternator itself were all OK. As primitive a test as that is, I think the alternator is OK too. I read on another Dodge forum a lot of other Dakota owners have 13.6 volts at the battery too so maybe that is how Dodge designed it. I read my Dakota FSM and Haynes book and they don't really mention much about voltage under operating conditions, just that it's not good to have less than 12 volts when the engine is running.

Besides cleaning up those 3 ground connections and the B+ connections at the alternator, I will leave well enough alone. It also dawned on me this afternoon that the reason why my gf's 4 cylinder Honda has a higher voltage at the battery could just be that she simply has a higher output alternator than I do. That would make good sense because her car has a lot more electrical accessories like a sunroof, power windows and locks, factory keyless entry, a nice sound system and really strong and freezing cold A/C. It has an automatic transmission that probably is electronically controlled and her car is probably a lot more heavily computer regulated and has more electronic gadgets and control modules running in the background than my plain old Dodge pickup truck with its old-school cast iron 6 cylinder and 5 speed manual transmission.

Thanks everyone for the help here.
 
Let us know if cleaning the cables helped.
13.6 is a bit low, but could be just how that particular regulator came out - a little low and a bit of bad luck.
 
I couldn't get to it today, too many honey-do's on the list. I did take a good look at the grounds in the daylight though, other than being a little dusty they all look fine. No corrosion that I can see. I also found another ground on the right side of the engine block below the alternator. The one main ground from the battery to the engine block is going to be hard to get to, the bypass hose for the water pump is right in front of it and there's not much clearance to work a socket or a wrench in there.

The other thing that I wonder is I have a new Duralast Gold battery, it is 750 CCA and is a really good battery. The old Auto Craft Silver that went dead only had 600 CCA's. I just wonder if I need a new alternator just for the simple fact I have a larger capacity battery now and need more juice to keep it charged. My truck has the stock 117 amp alternator, but there is a 136 amp alternator option. It's only $20.00 more for the 136 amp model.
 
Even new factory cable ends can have paint [an insulator] that is not cleaned off. It is not only corrosion that is a concern.
Do this once right, and be set for years.
Porsche and VW had regular problems with this.

Also, check the voltage drop along the cables - it is real easy.
All you do is take a common multimeter and measure the voltage at either end. Over a tenth or two means high resistance.
Sometimes an ADDITIONAL cable can be implemented with great results.
 
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