12V discharging problems on the Ford Focus Electric

I just made the last payment on my Ford Focus Electric (FFE). I’ve had it now for five mostly-wonderful years. But there’s been an occasional problem related to the 12V battery and I’ve finally figured out (most) of the details about it. If you have an FFE, you probably want to read this.

There are two batteries in the FFE: the big 325V 24kWh drive battery and the standard automative 12V (approximately 0.4kWh). The 12V gets recharged from the drive battery via a DC to DC converter because unlike a standard car there’s no alternator (and no engine to drive an alternator). In normal operation, the 12V’s charging cycle goes something like this:

  • Push Start button – 12V provides power to the computers and systems that turn the car on.
  • While the car is on, the DC to DC converter keeps the 12V battery charged similar to how an alternator would.
  • When you shut the car off, the 12V battery stops being charged, and it’s used to keep power trickling to the car’s computers and electronics in sleep mode.
  • When you plug in to charge the drive battery, the 12V usually doesn’t get charged unless it’s low – in which case the DC to DC converter will charge it just like when the car is on (I wrote more on this in an earlier post).

Typically the drain on the battery when the car is shut off is pretty minimal. I’ve had my car sit in long-term parking at the airport for a week or so and start up with no problems. But, sometimes the FFE can get into a bad state where it will drain the 12V battery at a much higher rate while the car is off. When in this state, the 12V will run down in approximately 48 hours, or less depending on the age and condition of your 12V battery. When this happens, you’ll come out to a dead car – the power door locks won’t work and the start button won’t work. When you charge up the battery with a trickle charger, it will start up fine and it will no longer be in the bad state! (To add insult to injury, when the car restarts it will then send you an email saying that the 12V battery is low!) Complete loss of power resets the electronics and clears up that bad state. So now you can drive it around just like normal and leave it unplugged for days and you’re fine – until the next time it gets into that bad state.

What I’ve finally figured out after years of having this problem crop up occasionally is that the trigger seems to be parking the car where it can’t get online and communicate with the cloud. For example, parking on the second basement level in my office garage means I can’t get satellite radio and there’s also no way for my car’s TCU (telematics control unit) to reach the online servers at Ford. Once that happens, the TCU or some related part of the electronics gets stuck in some state where it’s draining a lot of power. Once it’s in that state, if you let it sit for a day or two, the 12V will likely be dead. You can prevent this by disconnecting the 12V for a minute or so and then reconnecting it. That will reset things just like it does when the battery totally dies.

There are a few ways to tell when your car gets into this bad state:

  1. It will stop sending you emails about charge state (e.g. the one that tells you charge has completed).
  2. The MyFord Mobile app won’t be able to sync with the car anymore. It has a “Last updated at” field on the main screen – that will stay frozen at whatever date your car got into the bad state.
  3. If you park somewhere that your car should go into “Value Charge” mode when you turn it off, it won’t – it will be stuck on “Charge Now” and you won’t be able to change it.

This all seems pretty simple and straightforward as I write this up, but it took me five years and several dead-car incidents to figure all this out. Now I carry a lithium-ion jump starter in my car in case it happens again, and I’m very proactive about doing the disconnect/reconnect thing whenever it gets into the bad state. (Plus I don’t park on B2 anymore!)

I had hoped that software upgrades would fix this problem. I had my dealer perform TSB 16-0024 which updated the software on the PCM, ABS, BECM, SOBDM, and TCM. The problem still happens after all those upgrades. They also updated the APIM (Sync) to 3.10 and that didn’t make a difference either.

While I’m glad I’ve figured this out and I expect that going forward I’ll be able to manage this and never wind up with a dead car again, I am very disappointed that the 12V battery is the weakest link in the whole FFE platform. I love the car in general. It’s loaded with high tech components and systems. And yet the most mundane part – the 12V lead-acid battery that’s been part of automobiles for 100 years – that’s the one that causes the biggest problems, and even their latest updates haven’t fixed it. I hope they will deliver a fix for it someday but I’m not optimistic, as the FFE doesn’t seem to get much of Ford’s attention. If only that would change….


12 thoughts on “12V discharging problems on the Ford Focus Electric

  1. Thank You! I have a 2014 FF EV. I came out to my car yesterday and it was dead, dead, dead. My usual habit is to plug in at night – but the night before, it had a lot of charge left, so I didn’t. I read your comments and ubered to Wal-Mart and bought a charger. I charged up the battery and problem solved!.

    The FIRST thing the car did when I started it up was to update MySync. So I believe your theory that an update during the night got caught in a loop and caused the battery to discharge is correct.

    Anyway, thanks for saving me a AAA call, a trip to the Dealership, and paying for whatever they found, Victoria

    1. I’m glad to hear it helped! One thing I’d also suggest, if that’s your original 12V battery, replace it. They only last a few years anyway and when it gets completely dead it shortens the life even more. Mine was about five years old and had gone through half a dozen of these dead car incidents and the battery was so far gone it barely held a charge for 24 hours. From now on I’m going to be replacing it every 3 years or so…..

  2. The 12v problem is caused by the poor design of the car relying on all the modules to shut down and go to sleep when told to do so. Problems arise when one or more modules misbehaves and doesn’t shut down. It took countless trips to the dealer and over 5 months to diagnose that my TCU and RFA modules were occasionally not going to sleep. The only reason the problem was ever found was that the problem became less intermittent until it was eventually a constant problem. There is no data-logging so no way to know which module didn’t shut down. A major design flaw IMHO. You have to catch it in the act with a “draw down” test. This is basically checking the load on the 12V battery 40 minutes after shutting everything down. hitting a fob button or opening a door wakes up the car and resets the 40 minutes you’d have to wait to check the current draw. Ford’s spec. is less than 50mA. I measured mine at 20mA. However a fully charged 12v battery would die in as little as 4 hours intermittently. As mentioned above it was eventually found to be the TCU and RFA modules not shutting down. It seems the TCU is often one of the culprits and costs in the neighborhood of $700 to replace. So if it causes problems again and pulling the fuse to reset it doesn’t solve the problem I will just have to live without the TCU.

    1. Yuck! Sorry to hear about this problem Triangles. Sounds like it definitely could be related to the problem I describe here, although I’m not sure why it would start happening more frequently, unless you were more frequently parking somewhere the car couldn’t get online. Hopefully pulling the fuse keeps working! Note that as part of a recall I did have my TCU replaced and I’ve had this problem both before and after that replacement, so I don’t think it’s a faulty TCU that causes it – more likely (as you noted) just faulty design.

      1. I’m in the same situation! but having read this, and a few other posts, i ordered a monitor to plug into my accessory port to monitor the health of the battery, and got a battery maintenance charger.

        What is the TCU? Sorry! I had my cable harness replaced at the local dealer last year, mine is a 2014.

        i TOO love the car, but the Achilles Heel of the battery problem makes it a dicey thing to rely on.

        I never get warnings about low 12v battery and have not in two years (i got mine used two years ago)

        Some times,after a battery incident, the AC comes on when i turn on the car and i have to immediately shut it off. think i tried to pull a fuse a year ago to make some problem go away.. will have to remember why i did that. frustrating but thanks for posting this.

      2. Sorry, i looked it up!! TCU. Thanks for this fantastic post and to the responders as well.

  3. FYI I am on my 3rd TCU and it has failed as well causing 12V drain. Not spending the money to replace it. Just pull Fuse F1 and all 12V problems go away… at least for now. The TCU in addition to handling telematics duties stores the value charging parameters and GO time parameters so these two functions also go away when deleting the TCU. I don’t know if I can post a link or not but see this forum link for detailed notes of my 12v woes myfocuselectric.com/forum/viewtopic.php?f=14&t=3812#p27615

  4. Update: I have had my F1 fuse pulled for 11 months and have had no 12V problems.

    I have found the solution to preventing the TCU from killing your 12V battery without sacrificing TCU functionality. I found a low voltage disconnect from Galley Power and wired it in place of the F1 fuse and have it set to disconnect power to the TCU if 12V battery voltage drops below 12.1V. It will reconnect at 13V, ie when you turn the car on. Details on the low voltage disconnect can be found here: http://www.galleypower.com/store/p9/GPC-1005B-R_-_LVD_with_Recessed_Selector.html It only draws 3.5mA and practically nothing at 0.26mA if it disconnects due to low voltage.

    1. @Triangles

      Would you mind uploading a picture of how you wired it? I’m thinking of doing the same since my 2012 FFE just started having the 12v issues.


  5. The 12V battery in my 2014 Ford Focus electric died after 3 years (in 2017). Now today, 3 years later, that one has died. [Of course – the limited warranty on the O’Reilly battery is 36 months!]

    As I installed the new battery, I measured the current draw and it was 3.4 AMPS (with the car OFF, no lights or open doors!) – no wonder my weary 3-year old battery died overnight. (NOTE: the charging cord was not plugged in overnight, since I had only gone 3 miles since the last full charge)

    When I got in the car & turned it on – the SYNC screen was in the middle of a maintenance update. After the update completed, the car is fine again with the new 12V battery. The SYNC update uses the TCU module (Telematics Control Unit) to get software updates and there is a Ford service bulletin about this problem:


  6. Hi Paul, I have a 2017 FFE, living in Costa Rica. Have been suffering with these problem. We live in an apartment building, the garage is in a 3rd floor (of 18). Where is the TCU located? Front or back of the car? Ask because the garage is semi open, so I figure out that maybe parking the car toward the roofless part or the garage will help. Thanks.

    1. Hi Roberto, I’m not sure of the exact location but I do believe it’s towards the front of the car. Unfortunately I couldn’t find a diagram after some quick Googling…

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