Possible battery drain issue

[BrakeFade]

If you have a voltmeter check to see if your alternator is charging. If you’re seeing anything under 13.5v with the car on, your alternator is going bad.

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[thompsje]

BMS automatically resets too if you let the car sit or do it via forscan. The whole high beam thing really isn't needed. Just let the car sit for 8 hours and it's done

I think this is partially true. IIRC, it needs to sit for 8 hours and be locked up. If the doors are unlocked it won't go into full shutdown for the reset.

 

[Skye]

I used a few terms earlier. I wanted to come back and explain those, if you were not already familiar.

Battery Management System (BMS). The purpose of BMS is to adjust the charging system as the battery ages. All batteries, as they charge and discharge, deteriorate. As the battery becomes older, the Body Control Module (BCM) changes the profile of the alternator and other systems to support it. Maybe the alternator increases the amount of charging voltage. Perhaps it charges longer. Maybe both. Resetting BMS lets the charging system know a new battery is installed, so it can adjust accordingly. Refreshing the BMS reference is somewhat like resetting the Oil Life Monitor (OLM); zeroing out the OLM lets the Powertrain Control Module (PCM) know the oil has been changed, so it can reset its counters and measurements.

Parasitic Losses. The following processes and features are enabled on virtually all of our vehicles, the moment we turn off the car:

- BCM battery State of Charge measurements
- PCM emissions evaporation canister checks
- Door proximity sensors and contacts
- Trunk proximity sensors and contacts
- Hood ajar sensor
- Door ajar sensors
- Trunk ajar sensor
- Telematics modem and vehicle cellular system
- Bluetooth (802.15) interfaces (if enabled)
- Wireless (802.11) interfaces (if enabled)
- BCM background functions
- PCM background functions
- Interior motion detectors
- Vehicle movement detection
- Vehicle slope change detection
- Remote Transceiver Module (Intelligent Access)
- Engine Immobilizer (Passive Anti-Theft System (PATS))

State of Charge (SoC). When the vehicle is shutdown, the BCM monitors the battery's SoC, for its health, condition and charged level. The BCM is aware of the charge and discharge cycles which have recently happened and that parasitic losses are now occurring. The SoC test and monitor process also works towards ensuring enough energy is available to later start the car. If the battery's power reduces to a certain level, the BCM will begin terminating processes and disabling unnecessary features that it directly controls. The BCM will become more aggressive as power continues to lower, to the point were it could put the car in deep sleep mode.

 

[Free Spirit]

I think this is partially true. IIRC, it needs to sit for 8 hours and be locked up. If the doors are unlocked it won't go into full shutdown for the reset.

Yes, lock the doors and let it sit 8 hours or longer. The BMS system actually causes issues at least in 15-17 and you can disable it pretty easily by removing the wire and then never have to worry about it again. Battery just gets full charging while the car is running vs variable charging which never seems to work

 

[Farkel]

BMS automatically resets too if you let the car sit or do it via forscan. The whole high beam thing really isn't needed. Just let the car sit for 8 hours and it's done

Letting the car sit for 8 hours, locked and with windows up, lets the BMS determine the battery's state of charge. Resetting the BMS sets the "days in service" (battery age) to 0. These are two different things; both are used in calculating charging strategy.

 

[Free Spirit]

Letting the car sit for 8 hours, locked and with windows up, lets the BMS determine the battery's state of charge. Resetting the BMS sets the "days in service" (battery age) to 0. These are two different things; both are used in calculating charging strategy.

Forscan solves that in .2 seconds lol. Stupid easy to do. Although you can't even choose a good agm battery in forscan, the options are all terrible. You either tell it some bs capacity or a good bit below the rated cca or a good bit above the cca. They really outta give more options since most people swap to the d4700. I also up the charge from whatever stock is which I think is 70% and go to 90-95% so it actually charges the battery near full.

 

[justa16yote]

Yes, lock the doors and let it sit 8 hours or longer. The BMS system actually causes issues at least in 15-17 and you can disable it pretty easily by removing the wire and then never have to worry about it again. Battery just gets full charging while the car is running vs variable charging which never seems to work

So would unplugging the battery current sensor fix the issue?

 

[justa16yote]

So update: did the BMS reset, let the car run for about 30 minutes yesterday. Went to start it today and it barely had enough power to turn the starter over, in dash voltage read 13.8V to 14.2V to 14.0V

 

[Johnny Rockit]

Any mice problems where you park the car?

 

[justa16yote]

Any mice problems where you park the car?

No, not that I know of

 

[Free Spirit]

So would unplugging the battery current sensor fix the issue?

I'd start by unplugging the amp and stuff and seeing if the issue persists. I'd also recommend a battery designed for it. (OEM battery actually says not designed for any accessories) Most of us go with the xa power d4700. Its bigger and holds more charge and lasts much longercaince fully dying won't damage it. But start with the extra stuff you have to see if that stops the draw. I had a draw and it ended up being my oracle headlights (Bluetooth was running 24/7 draining it) swapped it to a fuse that's only hot with the engine on and fixed it. You gotta find the draw it can be anything. My boss had a draw on his Chevy, ended up being the wiring harness for heated mirrors (he never had heated mirrors but the factory includes the harness for options instead of redesigning the harnesses) you could have a funky harness somewhere. I'd check. The draw and while watching it pull fuses 1 by 1 and see when the draw stops and go from there

 

[5doorsoffury]

ok so ive fixed many drain issues. i do a parasitic load test. close the latch on the driver door so it can stay open with out the car knowing. take a digital multi meter and set it to amps. put the positive battery cable in series with the meter . lock the car and wait. you will see the draw go down as modules go to sleep. now if the drain is above 30ma you start to pull fuses until you find the circuit with the draw. i had a bad door pin on a customers car keep the bcm awake killing the battery. hell my dash cam in the mustang tapped off the cigg lighter never shut off. it killed my battery for weeks until i did this test and saw it. a 5ma resr current is ideal. for example a 20ma draw will kill a car in a week. a 40 ma draw 2 days and above that is a daily ordeal. so if u get down to the 30's id be cracking a beer with a smile on my face.

 

[FUN2RIDEFAST]

I have a 2016 Mustang GT, car has 132k miles on it. Recently been having an issue where if the car sits for longer than a day, the battery dies. Recently replaced battery and car sat for 2 days, and had no power, what could the issue be? Only thing aftermarket wired up is my amp/sub setup, and also I noticed when I do drive the car, on startup some of my sync settings defaults back to the original setting

If the trunk is open enough to turn on the light that'll do it because it doesn't shut off after a set time.

 

[The Spider House]

Did you do a BMS reset when you replaced the battery. I am not saying that is necessarily your issue, but it would be a good first step.

Is BMS reset something that also needs to be done when the ORIGINAL battery has been disconnected and then connected again? Is the procedure you described the same for all years in the S550 range? I have a 2022. Thanks in advance

 

[Farkel]

Is BMS reset something that also needs to be done when the ORIGINAL battery has been disconnected and then connected again? Is the procedure you described the same for all years in the S550 range? I have a 2022. Thanks in advance

I don't think so. The reset is only done to let the system know (or think) the battery is new. That parameter is stored and kept even if the battery is disconnected. Otherwise, it wouldn't need to be reset when replacing the battery.
The procedure is the same for all S550s.

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