I know we've all encountered features on new cars that seem like excessive over-engineering, and items that solve problems that never existed. As a Mustang owner, this one made me shake my head until I was dizzy.
If you replace the battery in a Mustang, the computer takes hours of uninterrupted 'thinking' to register the new charge state of the battery. If your battery dies, and you replace it with a fully-charged battery, crank it up and go for a drive, the system will actually overcharge the battery until it learns the new voltage level. Additionally, if you hook a charger / maintainer to the positive and negative terminal of the battery, instead of using the ground connected to the strut tower, the computer won't recognize the new charge state of the battery, and will charge the battery at next startup as if the battery were still at a low-voltage state. If it's already fully charged, it will overcharge it. Connecting the charger / maintainer to the positive terminal, and the strut tower ground is alleged to give the computer the information it needs, as it apparently makes a note of incoming charge through that ground cable.
I guess this is what carmakers are calling" progress". A 'smart' charging system that is too dumb to recognize the real-time charge state of the battery, and therefore, overcharges it. This isn't isolated to Ford....apparently GM employs a similar system. So, when my Mustang sits in the garage untouched for a month, I've been charging the battery using the negative and positive terminals. Sometimes I take it for a drive, sometimes I close the hood and don't touch it again for a month. It's good to know that during the times it was taken for a drive, the alternator was charging a fully-charged battery. Head ---->Brick wall.
From The 2020 Mustang Service Manual
Battery Charging
When charging the vehicle battery by connecting the charger to engine or chassis ground, the negative charger clamp must be connected to an unpainted chassis surface or a solid engine component such as a generator mount or engine lifting eye. In this instance, after charging, the BMS Reset is not required. Through this method of charging the BCM updates the battery state of charge during the charging process.
When charging the vehicle battery by connecting the charger to the negative battery terminal is necessary, such as when using a combination battery charger and battery tester/analyzer, like the GR 1 190 V3.0 Intelligent Diagnostic Charger, the BCM does not immediately update the battery state of charge. In this instance, the BMS Reset must be carried out using a diagnostic scan tool. This reset is needed for proper engine off load shedding and to prevent invoking of engine off load shedding earlier than normal.
If the reset is not carried out, when the battery is charged by connecting the charger to the negative battery terminal, it takes approximately 8 hours for the BCM to learn the new battery state of charge.
During this 8 hour period, the vehicle must be undisturbed, with no doors opened or keyless entry button presses. If the vehicle is used before the BCM is allowed to learn the new battery state of charge, engine off load shedding can still occur and a message may be displayed.
If you replace the battery in a Mustang, the computer takes hours of uninterrupted 'thinking' to register the new charge state of the battery. If your battery dies, and you replace it with a fully-charged battery, crank it up and go for a drive, the system will actually overcharge the battery until it learns the new voltage level. Additionally, if you hook a charger / maintainer to the positive and negative terminal of the battery, instead of using the ground connected to the strut tower, the computer won't recognize the new charge state of the battery, and will charge the battery at next startup as if the battery were still at a low-voltage state. If it's already fully charged, it will overcharge it. Connecting the charger / maintainer to the positive terminal, and the strut tower ground is alleged to give the computer the information it needs, as it apparently makes a note of incoming charge through that ground cable.
I guess this is what carmakers are calling" progress". A 'smart' charging system that is too dumb to recognize the real-time charge state of the battery, and therefore, overcharges it. This isn't isolated to Ford....apparently GM employs a similar system. So, when my Mustang sits in the garage untouched for a month, I've been charging the battery using the negative and positive terminals. Sometimes I take it for a drive, sometimes I close the hood and don't touch it again for a month. It's good to know that during the times it was taken for a drive, the alternator was charging a fully-charged battery. Head ---->Brick wall.
From The 2020 Mustang Service Manual
Battery Charging
When charging the vehicle battery by connecting the charger to engine or chassis ground, the negative charger clamp must be connected to an unpainted chassis surface or a solid engine component such as a generator mount or engine lifting eye. In this instance, after charging, the BMS Reset is not required. Through this method of charging the BCM updates the battery state of charge during the charging process.
When charging the vehicle battery by connecting the charger to the negative battery terminal is necessary, such as when using a combination battery charger and battery tester/analyzer, like the GR 1 190 V3.0 Intelligent Diagnostic Charger, the BCM does not immediately update the battery state of charge. In this instance, the BMS Reset must be carried out using a diagnostic scan tool. This reset is needed for proper engine off load shedding and to prevent invoking of engine off load shedding earlier than normal.
If the reset is not carried out, when the battery is charged by connecting the charger to the negative battery terminal, it takes approximately 8 hours for the BCM to learn the new battery state of charge.
During this 8 hour period, the vehicle must be undisturbed, with no doors opened or keyless entry button presses. If the vehicle is used before the BCM is allowed to learn the new battery state of charge, engine off load shedding can still occur and a message may be displayed.