How-To: remove and replace your 12v battery - recommended at 36 months

[dtbaker61]

I ran my original battery 39 months... tested shortly before 36 months hoping for warranty replacement, but it still tested ok. 'Great' SoH in fact... So I thought I'd charge to 100% and test monthly until it had a problem; thinking that since these little batteries are not cranking a starter they might last a lot longer than 36 mo warranty.

They don't ;(
They can fail suddenly, and without warning....

Possibly leaving you stranded somewhere if you are not prepared. I was lucky mine failed while I was at a jobsite in town and not out at one of my jobs in the booneys. I drove to the site, got out of the car, and the doors locked behind me! PAAK 'unlock' didn't work, Door pillar code bar did not 'light up', so I was stuck. Thank God I had my phone in my pocket and not locked inside the car!

Fortunately, I had several 12v batteries at home (for my solar business), and my wife was able to bring a battery, and a set of jumper cables to get me back on the road...

- used the spare 12v and the front bumper access port connections to pop the hood​

- jumpered the spare battery to the MME connection points, which was easy since I have access holes over the 12v+, 12v-, and HV disconnect. but, I ended up popping off the drivers side beauty cover so I could close the hood over the jumper cables.​

- and was able to start the car and get to my dealership, where they had a h3 35ah battery on the shelf ($211 + $16 core charge)​

I *could* have run with the spare jumpered in if a proper replacement was not available, but I'd recommend to anyone that when you battery hits 36 months, you ought to contact your dealership to make sure they have a replacement on the shelf, and consider scheduling a mobile service replacement or carry it with you, along with jumper cables to make the swap yourself.

So, being a diehard DIYer, I thought I'd document the remove-replacement procedure in case anybody else wants to be prepared to handle it without a tow to a dealership.

=============== DIY remove-replace the 12v ===========

removal procedure starts in service manual page 1999-2001
section 414-01, if you want the factory pictures. The process is:

- remove rear and side 'beauty covers'
- remove Tub - mostly 10mm, and a screwdriver to pop access panels
- remove cross brace - 18mm
- remove/replace battery - 10mm
- reset BCM with dealer 'Scan Tool' , or, follow 'home reset procedure'
Resetting tells the computer you have a brand new battery at 100% heath.


Reset new battery ONLY after charging it to 100%.
The easiest way to charge the new 12v to 100% is:

- turn MME ON
- Turn Vehicle>Settings>auto-off = DISabled
- turn Headlights, A/c, Heat, fan OFF
- .... and leave MME on overnight
- ODB2+Carscanner, or voltmeter, should verify that battery is 100% and
resting at 'float' voltage of 13.2v by morning

THEN, you can 'reset' the BCM to the new 100% capacity by:

- turn MME 'off' once LVB has been charged to 100%
- Press the START button without pressing the brake (ACCESSORY mode)
- Flash the high beams with the stalk 5x
- Press the brake pedal 3x
- Battery icon on instrument cluster should flash 3x to indicate reset
- Turn OFF the car
- Turn OFF Fordpass and Bluetooth if you use PAAK so car-phone are not communicating
- Park the vehicle undisturbed for 6+ hours to allow the BCM to verify the battery SoC and quiescent load


and here are the pictures... I pulled the cross-brace and Frunk Tub per service manual, but I think you may be able do the job just removing the cross brace and rear beauty cover

 

[Phil-Springs]

Wow, a DIY 12v replacement is going to take over 7 hours.. uggg.

 

[dtbaker61]

Wow, a DIY 12v replacement is going to take over 7 hours.. uggg.

no.... I'd say more like 1/2-3/4 hr to pull the tub, 15 minutes to remove/replace the 12v, and another 1/2hr to replace the tub and covers.

 

[Bikespace]

Zero microfiber towels were harmed in the making of this post.

 

[dtbaker61]

Zero microfiber towels were harmed in the making of this post.

it was an emergency repair, had to get back to work in AM, and I drive on a lot of dirt roads....

 

[Phil-Springs]

no.... I'd say more like 1/2-3/4 hr to pull the tub, 15 minutes to remove/replace the 12v, and another 1/2hr to replace the tub and covers.

Counting the home version of the battery reset taking 6 hours

 

[dtbaker61]

Counting the home version of the battery reset taking 6 hours

no need to count that .... you can remove/replace the battery in less than 2 hours of actual work, leave the car 'on' the next day to charge the new battery to 100%, do the reset, and let it sit overnight.

the replacement, charge, and reset do not have to be all at the same time. the charge/reset can happen anytime 'within a few days'. All it does is reset the battery capacity number of days in service and expected capacity back to 'new'.

 

[heisnuts]

I wonder what the local Ford dealer is going to quote for the customer pay replacement on the 12V battery.

 

[Just Lurking]

Nice write-up and photos; thank you!

I wonder if the recent software updates which changed the 12V charging logic will extend the life of the 12V battery? Older cars like yours may have had too much wear to benefit, but newer Mach-Es that spend most or all of their life with the new software may have better luck with their 12V battery.

Along those lines, my car is about 18 months old but I've charged mostly via L1 (on average charging every 1-2 days) which has provided lots of opportunity for my 12V to stay well charged. I wonder if that will help my 12V battery longevity.

 

[Blue highway]

when you checked the SOH last week, I presume the battery was connected to the car. Does this in some way make the SOH estimate optimistically high?

 

[leeman]

Wow you have to be an expert and removing plastic tabs and plastic shielding but now you have to replace the internal battery I guess it's no better than a gas power vehicle and maybe worse but what a process to replace a battery

 

[bshaw]

Counting the home version of the battery reset taking 6 hours

Why not flip the steps and use a trickle charger to bring the new battery up to 100% before starting anything else?
Then do the install and reset BCM to 100% immediately.

 

[2FlyMache]

I wonder what the local Ford dealer is going to quote for the customer pay replacement on the 12V battery.

My battery just failed. Dealer came to house and replaced battery in my garage for $265. Took an hour

 

[HuntingPudel]

no.... I'd say more like 1/2-3/4 hr to pull the tub, 15 minutes to remove/replace the 12v, and another 1/2hr to replace the tub and covers.

If you're good at pulling the tub, you can do it in <20 minutes. I spend more time chasing clips that fell into the car.

 

[dtbaker61]

Why not flip the steps and use a trickle charger to bring the new battery up to 100% before starting anything else?
Then do the install and reset BCM to 100% immediately.

certainly a possibility if you had the battery ahead of time.... I got it straight off the dealer shelf where it had been sitting for 2 months. I had to swap it in that day to be 'fixed' for work the next morning.

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