I've seen there "technicians" test batteries in duel battery set ups without isolating each battery, resulting in a false pass. They can test the alternator as well. But I have also had bad alternators pass on their bench.

 

Disconnect and charge both batteries, leave them sit overnight and check the voltage in the am. They should be fully charged and within .5v of each other.

A caution about "tests" at AdvanceAuto (maybe Autozone is the same, don't know?). They attempt to use a digital estimator to test the batteries and call it a "load test"

Unfortunately, this type of testing does not catch all defective batteries. The leads are not even large enough for a 100amp load test, let alone a 150-200amp test.

I recently had a defective battery drawing down my system and the good battery after only 4 months (Gold version). I could load test it and by disconnecting one battery at a time prove it wasn't holding its capacity, but their machine said it was "good"

In all fairness, all my own voltage based testing didn't find any problems, either. Just under heavy load or extended draw it faltered.

I disconnected one battery at a time and cranked it over. I had a bad starter I didn't know about that really pulled the amps and made the difference in the batteries quite obvious.

By all means, continue testing whatever you can and use these shops' equipment as possible. Just don't depend 100% on their results if they don't find a fault. Maybe 80%

You KNOW there is a fault somewhere. Hope you find it soon.

 

So after the truck sitting over night I checked both batteries in series and together they read 12.52 at the terminals and cables and at the alternator charging post. Disconnected the passenger side battery reads 12.51 and the driver side battery reads 12.54 does this tell me anything about the batteries?

 

No. Had they sat over night disconnected you may have seen a greater difference which perhaps may have been a tell-tale sign. Here are some other things, many of which you have already seen. Perhaps this will assist in your endeavors.

BATTERIES:

Tools: DVOM, Carbon Pile Tester or Similar Device, Hydrometer.
Charging system problems often come to you as a "no-start" complaint.

The battery will have discharged and the starter won't crank the engine. The first step is to test the battery and charge it if necessary.

No-Load Test:

Voltage Percent Charge
12.60V - 12.72V 100%
12.45V - 12.71V 75%
12.30V - 12.44 V 50%
12.15V - 12.29V 25%
(Readings obtained at 80°F)

STARTER MOTOR — LOAD TEST

NOTE: The batteries must be Fully charged before performing a starter load test.

1. Set the parking brake and shift the transmission into the NEUTRAL position.

2. Remove Fuse 17 from the engine compartment fuse box.

3. Connect the Alternator, Regulator, Battery and Starter Tester (ARBST). Follow the manufacturers supplied instructions.

4. Connect a remote starter switch across the starter relay Terminal and the battery positive terminal post.

5. Turn the ignition switch to the RUN position.

6. Crank the engine and record the voltmeter reading.

7. Turn the carbon pile control **** until the voltmeter indicates the same reading recorded during cranking the engine. Record the ammeter reading.

8. Compare the ammeter reading with specifications.

STARTER MOTOR — MOTOR FEED CIRCUIT VOLTAGE DROP TEST (7.3L)

1. This test is performed to determine if slow cranking is caused by high resistance in the starter motor circuit wiring.

2. The voltage drop test can only be performed with the starter motor on the vehicle.

3. Disconnect the wiring from the fuel shutoff solenoid.

4. Connect the positive lead of the 73 Digital Multimeter to the battery positive (+) post, and the negative lead to the starter solenoid Terminal.

5. Connect a remote starter switch between the starter solenoid Terminal and the positive battery terminal post.

6. Press the remote starter switch and record the voltage reading.

7. The voltage reading should be 0.5 volt or less. A reading higher than
0.5 volt indicates high resistance.

8. Repeat the test on the starter solenoid B-terminal.

9. If the readings are higher than 0.5 volt, remove the wiring from the starter solenoid.

10. Clean and inspect each wire connector and the starter solenoid terminals.

11. Install the wires onto the starter solenoid and retest.

12. If the reading at the starter solenoid M-terminal is still higher than 0.5 volt or the reading at the B-terminal is lower, carry out the Starter Solenoid Component Test. If no change is noted, install a new positive battery cable lead.

STARTER MOTOR — MOTOR GROUND CIRCUIT VOLTAGE DROP TEST (7.3L)

NOTE: A slow cranking condition can also be caused by high resistance in the ground circuit.

1. Disconnect the wiring from the fuel shutoff solenoid.

2. Connect the Digital Volt-Ohmmeter positive lead to the starter motor housing.

3. Connect the Digital Volt-Ohmmeter negative lead to the battery
negative (-) terminal.

4. Connect a remote starter switch between the starter solenoid Terminal and the positive battery terminal post.

5. Press the remote starter switch and record the voltage reading.

6. The voltage reading should be 0.2 volt or less. If the voltage reading is higher, remove and clean the negative cable connections at the battery, starter motor and the body.

7. Retest the system. If readings are still higher than 0.2 volt, test each individual negative cable.

STARTER SOLENOID (7.3L)

1. Disconnect the battery negative cable.

2. Using the Digital Multimeter, check the windings of the solenoid as follows:

a. Measure the resistance between the starter motor ground terminal and the solenoid case. The resistance reading should be approximately 0.95 ohms.

b. An extremely high resistance reading indicates a break or fault in winding continuity.

c. A very low resistance reading indicates a short or ground in the winding circuit.

*Either condition is cause for installation of a new solenoid assembly.

RIPPLE VONTAGE:

1. Ripple Voltage Ripple voltage or (AC voltage) can be measured by switching your DMM to AC and connecting the black lead to a good ground and the red lead to the "BAT" terminal on the back of the alternator, (not at the battery).

2. A good alternator should measure less than .5 VAC with the engine running. A higher reading indicates damaged alternator diodes.

ALTERNATOR LEAKAGE TEST:
Alternator Leakage Current to check alternator diode leakage, connect the Multimeter in series with the alternator output terminal when the car is not running. Leakage current should be a couple of milliamps at most; more often, it will be on the order of 0.5 milliamps. Use care when disconnecting the alternator output wire; make sure the battery is disconnected first.

Hope this helps,

Tom

 

^^What Tom said ^^

Plus, your batteries should NEVER be connected in SERIES, that would make 24 volts and likely hurt a bit

They are connected in PARALLEL to increase the Amps, not the Volts.

You probably already knew all this, but if someone else reads that and makes a mistake, it would be...not good

That's also why you can separate them and even run on one battery as a test, still 12v.

 

My bad I meant parallel! Lol

 

I do all the work on my truck and the problem is some of these tests are a little too much for my knowledge right now and I don't have some tools required. I do have a DVOM and wrenches but thats about it. The truck will run and start fine all the time but if I stay idling with the ac thats when the batteries start to run down. If I dont use the ac it will be fine and crank right up. The reason the truck died 2 days ago was because I was idling in line at Starbucks for 25 minutes with the ac on!! I just feel like if it was the battery why wouldn't it drain down while sitting for a while but it drains down at idle once it gets a load on it? I will disconnect the batteries tonight then check the voltage in the morning of each battery. Do I have to disconnect both or can I just remove the passenger side battery? I dont like messing with the connections much because then they become loose and dont charge at all

 

One more thing! When I charged the batteries fully to I believe it read 14.6 on each? As soon as I started the truck and checked voltage the alternator was still at 13.7 volts and actually ran the batteries down to that voltage slowly

 

I've purchased starters from DB Electrical, and one of their 165 amp alternators (one with the external rectifier kit). Their Denso-"style" starters are not worth the money and simply do not hold up reliably (at least, not for me). Their alternator has been running on my truck for well over four years (over 80K miles) without a hitch (so far).

My next electrical purchase went to Nations Auto Electric where I purchased a 3-bolt Mitsubishi starter and a 185 amp alternator for my wife's Excursion (I actually put the Mitsu starter on my truck and found a genuine Nippondenso starter locally for my wife's truck). Both the alternator and starter have run without a hitch for at least three years as well on the Excursion (sits a lot and only gets 8-10K miles per year, mostly short runs in town at less than 5-6 miles per run (each way).

That being said, the electrical strain is much worse on the goods I got from Nations due to the perpetual short-tripping and long sits between runs (1-4 days at a time), and their components have proven themselves to me.

 

Parallel...yeah, I figured it was a typo

Your terminals shouldn't become loose with use. After loosening them, I use something to pry them open just a bit, then remove them. Maybe that will help?

Any connection you leave on the battery reduces the certainty of your overnight drain test. I have one positive terminal that is a smaller size bolt and a pain. I have left that on, but removed the other positive and both negatives and called that "good"

Batteries when freshly charged start at a higher voltage, then equalize down to the voltages Tom mentioned. Give them a few hours to stabilize and you should see those.

In any case, you are looking for one battery that drains faster than the other. With such large batteries and not really any load, they shouldn't drop below fully charged overnight. One might. If one ends up after about 8hrs more than .2v lower, you may have found 'one' problem. It could be multiple

A question. Do your batteries ONLY drain with A/C running (and idling)? What about when your headlights and foglights are on and other accessories are running?

Trying to rule out the mag clutch of the A/C and wiring...

In my experience with a number of different situations beyond the Ex, electrical problems are as much about what you rule OUT as it is that you've narrowed it down to

Not always fun, but it IS POSSIBLE to find and fix. Hang in there!

 

I will check to see the exact voltage drop of everything today but I say the ac because that adds a .4 voltage drop so instead of charging at 13.6 volts it then drops to 13.2 volts and thats where they start draining. I have hids so I dont think they add much strain and no fog lights. I think I may just buy a alternator anyways since the original is on the truck and looks a tiny bit "burnt"

 

So I let the truck sit for 4 days, now I didnt disconnect the cables but the voltage sat at 12.45 and cranked fine when I started it this morning. Usually the voltage would be at 12.5 so I dont think I have a bad battery. I have a db alternator on the way and will let you all know what the results are when I install it. Hope it fixes it!

 

This is going to sound a little out there but my truck did the same thing, would not hold a charge and would not start unless I let it sit for a while. Replaced the alternator about 3 times in a year. Then I replaced the fuel pump at the same time I replaced the alt. and had 0 problems since. If you have 150000+ miles and haven't replaced it (and are willing to pay $100+ for an oem pump) I'd say go for it. Unless of course you can hear it pumping perfectly fine when you turn the key to the on position. Just speaking from personal experience.

 

My problem turned out to be a bad alternator and regulator. Drove me nuts.

 

It has been replaced before but it does sound a little knarly, not a smooth pumping sound more like almost grinding. But it's still pumping. I dont have trouble starting just my batteries decharging only at idle. But thanks for the input