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Had to Jump Start...Bat?? Let's Troubleshoot

galaxy

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Welp, so this is a first for me. First time she let me down and stranded. And it came uber surprisingly quick too...IDK.

Been sitting for about two weeks, but plugged in on the charger (green light) the entire time. I am religious about plugging in the battery, no matter low long or short it sits.

Was out running some errands to day. Car driving 100% normal. Completely great. First stop, the restart was juuusssttt barely enough to garner a slight look and a "what was that?". But nothing more. All normal and off I went. Second stop, for lunch. Come out, no dice. Cranked and cranked, but cranking rapidly slowed down and thus no start.

Pulled out the AntiGravity microstart and she jumped right off, zero issues, no long cranking, no delay. Completely normal start. But here's what I want to inquire about because I darn near never monitor my voltage, thus IDK.

I took the long way home, about a 40 min drive with a mix of town and freeway. This time monitoring voltage. Here's the overall of what I observed during the drive;

> Normal steady state driving voltage 12.8 +- .2. Note, RPM had zero bearing on voltage.
> Decelerating from any speed, voltage up into the 14's.
> Idle voltage 12.2

Here's what I thought was weird...throughout the entire drive of mixed condtions, I could change the voltage between the three stated conditions with the throttle at will. Let off the gas, voltage up in the 14's. Touch the gas, back down to high 12's. Idle, 12.2 religiously.

The only outlier was, once I got home, idle was 12.2. Turned on max AC, idle went up to 13.1. Turned off AC, idle dropped to 12.6 and stayed there rock solid. Never went back down to the 12.2.

Let the car sit for 20 minutes and restart. The restart was probably a 90% normal crank/start. Voltage was immediately at 13.5 for 20-30 seconds or better, and then right back down to 12.2.

Any thoughts?

Oh yeah, throughout today and throughout all time previously...completely normal car. No lights, no other electrical symptoms, no bugs, no gremlins, nada.
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jmn444

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original battery? Mine is a 2019 and already needed a new battery, the oem one is "lightweight" ish and lower cca's, I swapped to a normal gt spec battery and all is well again.
 

glockholiday

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If it's the original 2017 I wouldn't spend any more time troubleshooting I would get a new battery anyways without these problems. Then with the new battery, monitor voltage. These aren't like older vehicles where an rpm increase means voltage increase just because the alternator is spinning faster.

I would put a volt meter on the battery while running, should be 13-14+ volts, then shut the car off, then a reading on the battery should be 12-13 volts. If you see that voltage drop with the engine off it means your alternator is working.
 
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galaxy

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It is the original battery. Five years old next month. As mentioned, it has lived on a tender religiously since day one. But yeah...I figured the battery is a fair place to start regardless.

Also, please correct me if I'm holding onto too much old school logic, but still...big picture, basic auto electrics, I would tend to think if it were the alt or such, there would be other problems and the car would not run long if not producing electricity.

ATX-20HD and a MMR mount...here I come, LOL.
 
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ZX3ST

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If you're seeing 14+ volts under any conditions, the alt is fine.

Your battery likely has a cell that's on the way out. It might even show fine at rest, but voltage tanks when you put a load on it. Betcha it fails a proper load test.

Mine's probably not far behind. Had an alt failure at Heartland Park a few weeks ago that dragged the battery down to single-digit voltage before the car threw the alarm. I don't expect this one's going to keep trucking much longer after that abuse.
 

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galaxy

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If you're seeing 14+ volts under any conditions, the alt is fine.

Your battery likely has a cell that's on the way out. It might even show fine at rest, but voltage tanks when you put a load on it. Betcha it fails a proper load test.

Mine's probably not far behind. Had an alt failure at Heartland Park a few weeks ago that dragged the battery down to single-digit voltage before the car threw the alarm. I don't expect this one's going to keep trucking much longer after that abuse.

You beat me to it! I was literally typing what you just wrote....Just came in...battery sitting static at 12.45, but like you said, that's probably less than half the picture. I'mma let it sit all night not on the charger and see what it does tomorrow, but like mentioned, just no use risking limping it around.
 

jmn444

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i'm pretty sure my car killed two starters due to the battery being too weak.. I think the heat from track pushed it over the edge and the low voltage caused the starters to fry... no issues so far since putting the new battery in.
 

Postal Bob

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My car acted just like yours before the battery died.Same slow start, and then next time dead. And I kept it on a tender whenever I wasn't using it. And the voltage was bouncing all over the place too.
Just replace the battery. These cars act real funky when the battery is on it's way out. Five years out of the original battery is more than most will get.
And btw, when you first put in the new battery, make sure you do the BMS reset. And for the first few days, you may still see the voltage fluctuating until the battery becomes fully charged. Even connected to the tender, you will see the new battery take a lot longer to become fully charged the first time. A week later my voltage readings finally stabilized after a 4 hour road trip upstate.
 

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galaxy

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Dead this morning. Wouldn’t crank without my external jumper battery. Once it started, idle voltage straight to 13.9.

It’ll be a week before I can get parts in and fix it. What’s the best way to let it sit?

Batt stil reads 12+ right now, so I’m guessing the car shouldn’t do anything goofy?? Or would you yank the battery and let it sit dead?
 

Demonic

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It can sit dead or even disconnected without issue.
 

JZTRK

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My 19R is always on the tender has 8,500 on the odometer I drove it to work no issue....left work no issue. parked at my sons school for 15/20 min got out to get him at the gate walked back up to the car got in hit the start button and NOTHING!!! I called my wife to have her bring me the jump pack. I put it on clicked it on and also nothing.... used my Mach E to jump it and it jumped to life charging at 13.6v drove it home zero issues. I started it up about 5 times and it fired every time no issues the next day I go to take it to work and it is dead dead fob would not even unlock it so I used the door key pulled the battery and took it to the dealer to get tested. a few hours later he called and said it passed the load test several times. I pick it up fully charged put it in the car and it did the same shit days later!!! I was so pissed I bought a Duralast gold from Autozone and have not had an issue since
 

Egparson202

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I’m not sure what it is with these batteries. They’re sketchy. Or maybe it’s something with the BMS that causes them to be so unpredictable and to pass tests but then fall flat later. Best to just replace it.
 

Vlad Soare

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I’m not sure what it is with these batteries. They’re sketchy. Or maybe it’s something with the BMS that causes them to be so unpredictable and to pass tests but then fall flat later. Best to just replace it.
I think it's because the BMS does its best to keep the battery in the best possible shape at all times, which may sometimes conceal some signs of impeding death. I imagine it's somewhat like a patient suffering from a terminal heart condition, who were connected to a device that sent small electric shocks through his heart to revive it whenever its activity slowed down. You would never know he's on the verge of death until he actually died, and then you would be surprised - he seemed so healthy yesterday...

If the battery is three or four years old, testing it from time to time isn't a bad idea, even if it doesn't seem to act up. If its health is declining, at least you'll see it coming.
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