Possible battery drain issue

[justa16yote]

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

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[MiamiGT350]

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.

 

[justa16yote]

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.

How do I do that?

 

[MiamiGT350]

How do I do that?

Procedure must be carried out within 10 seconds:

1. Switch ignition on (engine off)
2. Pull and release high beam 5 times.
3. Press and release brake pedal 3 times.
4. If successful the battery light will flash 3 times within the next 15 seconds
5. BMS reset completed.

 

[Skye]

Other than the new battery, any recent changes to the car?

Any recent maintenance?

Is the car generating any events or alarms in the dash?

What voltage level is registering in the in-dash display when the car is being driven?

Before this last week, when was the battery previously replaced?

How often is the vehicle driven? When it is driven, how long?

A Battery Management System (BMS) reset would help; this zeros out the charging system's reference point. Should be done each time the battery is replaced. Simple to do.

Take a moment to do a general check of cables and connectors. Look at the battery, alternator, the trunk connections for the audio, etc. Put your hands on things, confirming those bits are connected well.

If you have the tools or abilities to check the alternator's output, do so. Confirm that, under an appropriate load, the generator is capable of supporting that, while charging the battery to. Some of us have the tools to do so. Many don't. Take a trip to the parts store or dealer and ask them to do a check. They can also review for codes via an On-Board Diagnostics (OBD) tool.

If the topics above appear in good working order, but you're still having problems, you can begin investigating any large parasitic draws.

Audio amps and the like can suck a lot of current. Something internal to those components or a setting might have changed. If the problem continues, I'd attempt to isolate the aftermarket components to the greatest extent possible, then monitor for changes. Pull a fuse. Disconnect a lead. Whatever.

If the problem continues still, you can begin pulling individual fuses in the car. While tedious, you can see where the current is going. Using an inductive meter would shorten the process greatly. With the meter on the car's battery cabling, it will display any electrical loads.Pulling one fuse at a time, monitor the drain. If you see a large drain but then it stops when the fuse is pulled, that's your problem circuit.

 

[Snakebyte]

Is it possible that a new electronics device was installed in the car? If so, maybe a power supply was tapped from a constant hot instead of a switched hot circuit. The company that installed my son's multimedia player for back seat occupants did that.
BTW...I use an OBD II power supply plug which has an off/on switch, giving constant power or switched power for my dashcam. If I fail to toggle the switch to from the constant power position to the switched power position I experience significant power drain over a couple days, similar to what you are experiencing. (I chose this switch type for easy constant power access should I need to park in a questionable location, or if I have a conversation with law enforcement that I may want documentation on.)

 

[justa16yote]

Other than the new battery, any recent changes to the car?

Any recent maintenance?

Is the car generating any events or alarms in the dash?

What voltage level is registering in the in-dash display when the car is being driven?

Before this last week, when was the battery previously replaced?

How often is the vehicle driven? When it is driven, how long?

A Battery Management System (BMS) reset would help; this zeros out the charging system's reference point. Should be done each time the battery is replaced. Simple to do.

Take a moment to do a general check of cables and connectors. Look at the battery, alternator, the trunk connections for the audio, etc. Put your hands on things, confirming those bits are connected well.

If you have the tools or abilities to check the alternator's output, do so. Confirm that, under an appropriate load, the generator is capable of supporting that, while charging the battery to. Some of us have the tools to do so. Many don't. Take a trip to the parts store or dealer and ask them to do a check. They can also review for codes via an On-Board Diagnostics (OBD) tool.

If the topics above appear in good working order, but you're still having problems, you can begin investigating any large parasitic draws.

Audio amps and the like can suck a lot of current. Something internal to those components or a setting might have changed. If the problem continues, I'd attempt to isolate the aftermarket components to the greatest extent possible, then monitor for changes. Pull a fuse. Disconnect a lead. Whatever.

If the problem continues still, you can begin pulling individual fuses in the car. While tedious, you can see where the current is going. Using an inductive meter would shorten the process greatly. With the meter on the car's battery cabling, it will display any electrical loads.Pulling one fuse at a time, monitor the drain. If you see a large drain but then it stops when the fuse is pulled, that's your problem circuit.

Other than the battery, nothing has changed to the car

Only recent maintenance was plugs, no events or alarms

In dash display reads 14.3V while my NGuage reads 14.5V

Previous battery was put in ~August of 2023

Driving it usually depends, maybe 3-4 days a week, usually to work and back (33 minutes one way) or about an hour away in some cases

 

[justa16yote]

Is it possible that a new electronics device was installed in the car? If so, maybe a power supply was tapped from a constant hot instead of a switched hot circuit. The company that installed my son's multimedia player for back seat occupants did that.
BTW...I use an OBD II power supply plug which has an off/on switch, giving constant power or switched power for my dashcam. If I fail to toggle the switch to from the constant power position to the switched power position I experience significant power drain over a couple days, similar to what you are experiencing. (I chose this switch type for easy constant power access should I need to park in a questionable location, or if I have a conversation with law enforcement that I may want documentation on.)

The only things that are installed is my NGuage, which is always plugged into the OBD II port, and my amp for my sub

 

[Skye]

I assume the replacement battery has at least as many CCA or more than the original unit.

I'd get the charging system checked first, confirm the alternator is working correctly.

The car is approaching 10 years of age, 120K miles. There's the audio load.

My in-dash display never shows lower than 14.5V. That yours is showing lower could be one tell.

Something else that interests me: the previous battery lasted only two years.

- Checking the charging system is often free and easy to get done. I think it's best to confirm the alternator is putting out all that it is supposed to.

- In the process of getting that checked and confirmed good, I'd keep in the back of your mind of a possible drain, something new. If your suspicions lead you to that, I'd isolate the aftermarket audio, disconnect all ancillary devices that might be running when the car is off, etc.

Hopefully, between those two paths, you'll quickly home in on whatever is going on.

 

[Snakebyte]

In addition to the BMS reset others have mentioned, the nGauge is my only other thought. I'm not familiar with nGauges, so I don't know what parasitic drain one could generate.

 

[Skye]

As @Snakebyte and @MiamiGT350 mentioned, the BMS reset. Before any more tests or checks, do this.

 

[justa16yote]

In addition to the BMS reset others have mentioned, the nGauge is my only other thought. I'm not familiar with nGauges, so I don't know what parasitic drain one could generate.

Now that I don’t know but considering that I’ve let the car sit for over a week and a half at one point with it still plugged into and it still fired right up, it’s probably not drawing anything when the car is off

 

[16Fastback]

Other than the battery, nothing has changed to the car

Only recent maintenance was plugs, no events or alarms

In dash display reads 14.3V while my NGuage reads 14.5V

Previous battery was put in ~August of 2023

Driving it usually depends, maybe 3-4 days a week, usually to work and back (33 minutes one way) or about an hour away in some cases

My brother unplugged my COBB while working with Forscan plugged in the COBB it turned on when plugged in drained my battery even with the battery tender charging if your NGuage is plugged in all the time t could be your problem.

 

[John S]

My son's audio system has a 10 gauge feed (w/inline fuse) tapped in at the positive battery terminal. If there are any parasitic drains on the electrical system, that's the first circuit I would be looking at. (Or any other non-switched circuits that could be acting up and draining the battery.)

 

[Free Spirit]

Procedure must be carried out within 10 seconds:

1. Switch ignition on (engine off)
2. Pull and release high beam 5 times.
3. Press and release brake pedal 3 times.
4. If successful the battery light will flash 3 times within the next 15 seconds
5. BMS reset completed.

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

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