Replacement AGM Battery?

Vlad Soare

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The BMS reset tells the BMS that the battery is new. It resets the battery age. This must be done anyway.
If you replace the battery with an identical one, that's all there is to it.
However, the BMS also knows the battery capacity and type (EFB/AGB) and uses this information to devise a suitable charging strategy. If you switch from EFB to AGB and/or to a higher capacity, then a bit of extra programming will also be necessary.





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PoCoBob

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This is from the 2019 GT owners manual. Sounds pretty simple

After battery replacement, or in some
cases after charging the battery with an
external charger, the battery management
system requires eight hours of vehicle sleep
time to relearn the battery state of charge.
During this time your vehicle must remain
fully locked with the ignition switched off.
Note: Prior to relearning the battery state
of charge, the battery management system
may temporarily disable some electrical
systems.
 

scotty

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That's interesting but I wonder if applies only to swapping in the same type/sixe/capacity battery?
The OP wants to go with an AGM type battery.
I kind of doubt that the car can determine from a simple reset like described that a different battery type is in use.
I just swapped to a group 47 AGM battery last month and used this method. It cleared all the "System off to save battery" messages that were still coming up after replacing the battery, so it seems to work fine.
 

NoVaGT

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There no reprogramming involved with switching a battery, just make sure you don't cross negative and positive..
Someone did that, and posted about it here. Recently.

I don't 100% remember the outcome, but I think it was one big-ass main fuse and all was well.
 

NoVaGT

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Tang

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FWIW I took out my old battery and replaced it with an AGM and didn't do anything special and the car was/is fine YMMV
 

plc268

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I reading this all like just letting the car sit for 8 hours is all that's necessary.
Yea. A BMS reset isn't required and the car will reset itself once you let the car sit overnight.

People are making it more complicated than it has to be.
 

19gtaz

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I wonder why Ford didn't use an AGM battery in the first place. They did on my 2018 F150 with 5.0 and it has much more underhood room and air circulation.
 

NoVaGT

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I wonder why Ford didn't use an AGM battery in the first place. They did on my 2018 F150 with 5.0 and it has much more underhood room and air circulation.
Because $9,463,259.82 of profit in each truck unit sold. Versus $.32 in each Mustang sold.
 

Vlad Soare

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Letting the car sit overnight will allow the BMS to relearn its state of charge. If that's all you want, then a BMS reset isn't necessary.

But that's just one part of the equation.

The BMS also knows the age of the battery and takes it into consideration when choosing the charging strategy. The age counter must be reset when you install a new battery, otherwise the BMS will treat your new battery as if it were old and will charge it accordingly.
I know of instances where some systems (particularly the stop&start, but also the heated steering wheel, or heated windscreen if fitted) had stopped working due to the load shedding caused by a weak battery, and they continued not to work after having the battery replaced. A BMS reset fixed that.

Here's the battery replacement procedure from the service manual.

Screenshot 2021-01-12 at 08.37.03.png


It doesn't say it's optional. It doesn't say that simply leaving the car parked overnight will do.
 

Elp_jc

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I wonder why Ford didn't use an AGM battery in the first place.
Take a wild guess. If it was 'cost cutting', it'd be the correct one :).

My car sat at a dealer for months, so my battery was toast, and didn't want another crappy wet cell, or to deal with a dealer, so bought a DieHard AGM OEM replacement (96R) at Advanced Auto out of pocket. Same specs as stock, so just reset the BMS, although it was probably unnecessary due to the car only being 6 months old.
 

19gtaz

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Take a wild guess. If it was 'cost cutting', it'd be the correct one :).

My car sat at a dealer for months, so my battery was toast, and didn't want another crappy wet cell, or to deal with a dealer, so bought a DieHard AGM OEM replacement (96R) at Advanced Auto out of pocket. Same specs as stock, so just reset the BMS, although it was probably unnecessary due to the car only being 6 months old.
I'm going AGM battery next time I need a battery. With all the cables going to the battery terminals I don't want any corrosion problems. Besides that the one's I've had lasted longer.
A lot more money but worth it to me.
 

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People are making it more complicated than it has to be.
That's the M6G way. Ask a simple question. They say the owner's manual must be wrong, you know, cause they never bothered READING it, then give you the most convoluted way to go about it. Haha. The BCM really doesn't give a hoot what battery you install as long as you let it be for 8 hours.
 
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PoCoBob

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Just me thinking out loud but my guess would be the dealer does the reset because they want the car to leave the shop with everything working as it should. Those of us who do things ourselves may loose some functions until we do the 8 hour sleep procedure. My cars less then a year old so I hope to not worry about this for a few more years.
 

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