I'm asking for opinions before I replace my batteries. Just to be sure I'm not missing some bigger picture as these trucks are more and more complicated.

Symptoms: Last evening after work my son was driving my truck home from work and the "cleaning exhaust filter" came on. He took the long way to get it some time. He on a highway probably going about 70. Truck is warm and everything is normal. The dash beeps and flashes a "Check Brake System" message. That's never happened before. He pulls over an calls me. Brakes seem to be fine so he continues home. While doing so the speedometer stops working. Shortly after everything dash related shuts down including radio. Truck still drove normal and he parks it at the house. I get in to check and everything is normal. No Check Engine Lights, no codes, no stored codes. Pretty much your standard dealer response of cannot duplicate the problem.

What I know: Batteries will test 14 something when running. 12.7 soon after shutting down the engine. 12.4 after sitting overnight. 12.01 after leaving the lights on for a few minutes. Goes back to 12.4 pretty quickly after turning the lights off. Voltage drops to 10.2 ish when starting but that is with a digital multimeter that doesn't react too quickly so I'm suspecting it's lower.

In my mind everything points to a low battery with the dash acting funny and what I think is low voltages from the batteries. But I'm no expert. Took it to autozone so they could test the battery. Guy says its good. I started it and their tester said bad starter that might be drawing a load. I don't know what to make of this. The truck starts quickly and without hesitation. Even if it sits for a few days. The date on both batteries are 11/18 so yeah they are about done. ( I did have an original Mortorcraft battery last in a previous truck a whopping 19 years!!!)

Just looking for any input before buying batteries when i should be replacing a starter. Or just wait to see if the problem repeats itself.

 

Have the alternator checked out before you buy batteries... I found this link...

https://www.thedieselstop.com/thread...issues.613897/

It has a Ford tech who says if the alternator is overcharging, the modules could be shutting down to protect them. Check out that link.

 

^^ check he charging system. A weak battery wont cause those issues since the charging system is what runs the truck while the engine is on. If fact once started, the batteries aren't even part of the picture other than being recharged. You can disconnect them both and the truck wont care.

 

A weak battery shouldn't cause this, but depending on the mode of failure the batteries can cause issues even if the charging system is good, but it is best practice to test both batteries and the charging system as they can effect each other and a bad battery(s) can take out a charging system, as a bad charging system can take out the batteries.

 

When one of my batteries was failing, I did get the check brake system message. Replaced both batteries and haven't seen that message since. Low voltage from the batteries can cause some strange errors.

 

I would check out the alternator also to rule that out...

 

This is on point, but don’t ever disconnect the batteries while the engine is running. The battery acts as a big buffer to limit voltage spikes and transients. You might get away with it once or twice but you could also fry in-vehicle electronics or even your alternator.

 

Good point. We see a similar issue when implementing LiFePO4 systems in RV's. The BMS on the battery decides it has had enough charge and cuts it off immediately. No ramp down, it's just off. That can cause a surge upstream. Usually it's seen as a semi-smart component that shuts down due to high voltage readings. I could see where a dumb component doesn't deal well with the voltage spike.

 

Given how old they are and the readings from your multimeter, I’d suggest replacing the batteries first. If the problem is low voltage from bad batteries, new ones could fix it entirely.

 

I understand the theory that a week battery shouldn't cause what I had and understand the alternator runs the vehicle after it is started. However a similar thing recently occurred with my son's Ford Edge. Weird stuff was happening, messages that made no sense. At least his symptoms kept occurring so it was easy to rule things out. In the end a new battery stopped all the issues. He old battery still tested good but wasn't great. So why the theory is sound it's not always the case.

Didn't get the condition to recreate itself yesterday. Going off FORSCAN the alternator was giving the truck what is was calling for. (Ranging from 14.12 to 14.28 volts during a drive) Ended up getting 2 new batteries just because. They were almost 6 years old and currently my son is driving it to school and work. I was planning to swap them out before a longer (12+ hour vacation drive late summer so it's only a few months early)

Son says the dash seems brighter but I'm not sure its for real or in his head.

I don't know if the issue was a fluke, battery related, or charging related. Only time will tell and I may never know.

 

What about checking the battery terminals? Seeing if they're tight? Maybe KISS theory...

 

Pull the batteries off the truck and let them cold soak. Check and see if they need to be topped off. If one or two of the cells aren't covered in water or corroded, I'd replace the batteries. This will also allow you to properly test them without the charge from the alternator. This is how I've found quite a few bad batteries that were "hiding" so to speak.

 

Good point, didn't consider the sensitivity of all the garbage in our vehicles today. Back when I was wrenching, cars only had good stereos, and GPS was a pipe dream.

IIRC there is a gadget on the negative terminals of the battery that measures battery information. Maybe somehow that is what triggers the issues. On my wifes Focus, that thingamajigger is setting a code, and is either corroded or went bad, just haven't gotten around to fixing it yet. If a battery is having a cell drop out, I suppose it could signal an low voltage trigger and cause the issues.