Battery or charging system issues?

[Free Spirit]

So I noticed for awhile I would get the system off to save battery message so I replaced my battery (battery would die every time it got coldish or sat for more than 1 days) got an xs power 4700 per alot of recommendations. No issues for a week.

A bit goes by and the messages come back but the car starts fine. But now it's maybe 6 months later and the temps are low 30s and highs of 60-80s here nn Pennsylvania. Car cranks super slow after sitting overnight to the point I think it's dead. 1 crank and then like 5 seconds before it'll crank again almost as if there's no power. Had a mechanic check the battery and alternator both are fine. The only other thing changes is state of charge was changed from like 70% to 90% and the battery type was changed to the closest size I could find for the new battery via forscan. When I installed it. Any ideas why the slow crank/dying battery.

Accessories are very simple, uniden r8 radar detector hardwired into the rear view mirror (shuts off when the cars off) and a viofo dashcam that turns to parking mode with the car off but turns off at a set voltage (usually I set it to 11.8 or 12.0). And it's hardwired into the fuse box on the passenger side. I have tried unplugged both and still have these signs. Per the cars instrument cluster voltage tonight reads 11.8 right after shutting the engine off and after having driven it for about 30 min from work to get gas and home. (Feel like 11.8 is already a bit low but I don't really know anything about batteries). I will update in the morning what the cluster reads when I put it in acc mode to check the voltage (with dashcam and radar detector both unplugged). Parked it at 5pm and will start it around 6am.

Please help me figure out this nonsense because when the temps drop below 30 im concerned it will need a jump every single time.

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[KeyLime]

Assuming your instrument cluster gauge is accurate, 11.8 V is really low after shutdown. I would also double check using a multi meter to make sure the cluster is correct.

 

[Paddles]

Did you perform the BMS reset after swapping batteries?

 

[jd_cobra]

^

As previous post stated, a BMS reset would probably help, along with turning off auto updates if you have them on, as they would put my car into BMS especially if I didn’t drive it frequently, causing a perfect storm if you will, for my battery to deplete and not charge back up properly.

 

[Free Spirit]

Did you perform the BMS reset after swapping batteries?

2times yes, one one by letting it sit for the many hours and then again with a forscan reset for it.
This morning (didn't get as cold low of like 50°) the cluster reads 11.7bafter sitting and did better/fine starting maybe just a tiny bit slow. Tmr/TN has a low if 60° or so so I'm going to do the same test, park it around 5

Assuming your instrument cluster gauge is accurate, 11.8 V is really low after shutdown. I would also double check using a multi meter to make sure the cluster is correct.

This morning (didn't get as cold low of like 50°) the cluster reads 11.7bafter sitting and did better/fine starting maybe just a tiny bit slow. Tmr/TN has a low if 60° or so so I'm going to do the same test, park it around 5after work and leave the dashcam and radar detector plugged in and see what changes from the cluster readout.

 

[Free Spirit]

Did you perform the BMS reset after swapping batteries?

2 times yes, one one by letting it sit for the many hours and then again with a forscan reset for it.

 

[Free Spirit]

^

As previous post stated, a BMS reset would probably help, along with turning off auto updates if you have them on, as they would put my car into BMS especially if I didn’t drive it frequently, causing a perfect storm if you will, for my battery to deplete and not charge back up properly.

Not sure how I turn off auto updates (if you mean for the sync 3 I had to force update it to a version not available from Ford via USB. But I did perform a BMS reset twice. One via forscan and one by letting it sit for the set amount of time I think it was like 8 hours or so

 

[jd_cobra]

It’s the settings menu of the sync system.

Here’s a link on the manual reset done on a F150, but it works for the mustang as well.

 

[KeyLime]

If your battery is reading 11.8 V right after shutting the engine off you have something other than a parasitic load. Either the battery is kaput or the charging system isn't doing it's job.

What is the voltage at the battery terminals with the engine running? If the battery is initially at 11.8 the charging voltage after start up should be at least 14.5 V, maybe higher as the system is trying to jam juice back into a heavily discharged battery. You should also check the voltage at the terminals after a long drive. The quirky on/off charging system in new cars will complicate this measurement but you should see about 14 V part of the time.

If you have a battery charger or tender you can try disconnecting the battery terminals and charging the battery overnight using the tender. Disconnect the tender and let the battery sit for a couple of hours then measure the voltage at the terminals. If the measurement is low then the problem is the battery.

 

[Free Spirit]

It’s the settings menu of the sync system.

Here’s a link on the manual reset done on a F150, but it works for the mustang as well.

Auto updates are off. Was done as part of my sync 3 upgrade and then force installed sync 3.4 because Ford never offered 3.4 for the year the system is from

 

[Free Spirit]

If your battery is reading 11.8 V right after shutting the engine off you have something other than a parasitic load. Either the battery is kaput or the charging system isn't doing it's job.

What is the voltage at the battery terminals with the engine running? If the battery is initially at 11.8 the charging voltage after start up should be at least 14.5 V, maybe higher as the system is trying to jam juice back into a heavily discharged battery. You should also check the voltage at the terminals after a long drive. The quirky on/off charging system in new cars will complicate this measurement but you should see about 14 V part of the time.

If you have a battery charger or tender you can try disconnecting the battery terminals and charging the battery overnight using the tender. Disconnect the tender and let the battery sit for a couple of hours then measure the voltage at the terminals. If the measurement is low then the problem is the battery.

I'll check when I get home tonight. It usually is 14+ V after starting as it tries to charge. I wonder if I should go back and change the forscan options back to default. I believe that since it is charging then the alternator is good (also had tested at mechanic and at an advanced auto to triple check) battery also tested fine both times but I might try to warranty it or something, would disconnecting the BMS help? I know it can be disconnected so the battery gets a constant charging and not a variation of charging voltages? Not sure what changed since it was mostly fine before. The only other thing is I fucked up a ground screw on the strut tower but I tried it and put a new screw in (terribly done but it's been holding and no codes) but that was a good bit ago before the issues with this new battery.

 

[KeyLime]

Did you figure out what the problem is?

 

[Free Spirit]

Did you figure out what the problem is?

No. And it spissing me off because I just went to get food just now. Cars been sitting since probably Thursday night. So 48 hours or less and dead. Barely cranked 1 time it was super slow then nothing. Car read 11.0V on the dash. Got it tested and it tests as battery good, charging system good, alternator good, starter says charge battery and then the odd thing (which could be that it still wasn't fully charged) it was rated at 769 CCA but tested at 540cca but it was def not charged yet I think. I have no clue. I doubt it's my dashcam as it turns off at 11.8-12.0 volts depending on my settings but I feel like the battery should last alot longer. Before needing a jump. The lows are in the 30s and it's only getting colder and I can't be jumping it daily

 

[RacingRoger]

I'm starting to get this message too...
My car sits for about a week at a time, and with it getting colder, it'll probably be driven less. My car is a '22, so battery is not over 3 years old (she was built 8/22). I'm just starting to get into the troubleshooting -- checked the water level on the battery and one side was a little low. Topped off with distilled water and all was good for a few days. Message is back, and my handheld voltmeter shows 11.6v. Guess I'll have to drive it again...

Free Spirit, did you ever get a good fix on your Mustang?

 

[Ras Thavas]

I'm also having this problem. I replaced my battery last year because of weak starting. I will hit the button, get one crank, then nothing for a second, then weak cranks. Because of the weather lately I have only been driving it about once a week.

Today I get in to drive it, weak cranking. It has probably been 10 days since I drove it last. Drive for 25 minutes to the store. Gauge, indicated 15V. Got out of the store and it almost didn't start. Watched the volt gauge all the way home, never strayed from 15V.

Just got done charging it with a battery charger and it starts fine.

When I previously replaced the battery I followed the instructions to reset the system.

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