PowerBoost F150 will run without engine battery hooked up...

[currybob]

This news makes an experience I had last month even stranger. I went out to go somewhere and.... the door won't open. Actually, the mirrors didn't pop out to greet me. What is going on? I use the hardware key to open the door and it is absolutely dead inside. No idea how or why, I had driven it the day before no issues. So I hooked up my little jumper pack and jumped it. Of course all hell broke loose, with the alarm and about a million warning messages on the console. (To answer the question of why there is still a 12v battery, I'm assuming so you can jump it when its completely dead.)

The most concerning issue here was there wasn't enough juice to release the auto-parking brake. I was absolutely stuck. I left it running in Tow-Haul mode for 30 minutes, and still it wouldn't release the brake. Stop engine, start engine, didn't matter. I kept getting an error about brake failure. I was able to get this solved by reading some older F150 posts with the brake error: Give it some gas in neutral to increase RPMs, and then hit the brake release, which worked. It's been a month so I forgot the specifics, but that was more or less how I got it all back to normal. And I haven't seen a complete discharge like that since.

So based on this thread, I somehow discharged both the 12v as well as the 48v battery completely, in less than 24 hours. The 7.2kw panel in the back wasn't being used, and I can't think of any other power draw that would have drained that much power.

You will need to take it to your dealer to have it checked out. You sure don't want to go through that again.

Taking mine in next week for the windshield fix and some other thing with the software and the heated mirror recall. Truck has been flawless except 3rd gear is starting to not be as smooth a shift as before. That is why I was trying to cut the power off to re-set the learn on the tranny, thought that would help. Will have them look at it while it is in for the other stuff.

I really love this truck, amazes me every time I drive it.

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[AaronA]

If there is a battery underneath the rear seat, its news to me (2021 F-150 PowerBoost). There IS a small inverter... but I don't think there is a battery.

There is a smaller 12V battery under the rear passenger seat. the cover pops off once you release a sprung tab. I had disconnected both this and the main battery to try and hard reset the entire system (which it did successfully, everything went dead), unfortunately my issues were related to poor Ford factory quality control and still had to go to the dealer for over a month (see my posts in HEV warning thread on the main power connector).

Obviously I wouldn't recommend using the powerboost without the main battery for engine starting, the smaller one appears to be used to maintain control power essentially, but somehow they have to be interconnected on the main electrical system. I'm still very curious about that if anyone knows!

 

[currybob]

There is a smaller 12V battery under the rear passenger seat. the cover pops off once you release a sprung tab. I had disconnected both this and the main battery to try and hard reset the entire system (which it did successfully, everything went dead), unfortunately my issues were related to poor Ford factory quality control and still had to go to the dealer for over a month (see my posts in HEV warning thread on the main power connector).

Obviously I wouldn't recommend using the powerboost without the main battery for engine starting, the smaller one appears to be used to maintain control power essentially, but somehow they have to be interconnected on the main electrical system. I'm still very curious about that if anyone knows!

I pulled the cover and spotted the 2 nd battery, I pulled the main battery cable under the hood and now no longer shows a current. I was trying to re-set the memory on the tranny shifting because the 3rd has been getting a bit clunky going into that gear. I let it sit for 45 min, hooked it all back up but did not change anything on the tranny.

Thanks AaronA

Having the windshield recall done next week and will have them look into this while it is there.

 

[PB2021]

I have a '21 Powerboost equipped F150 and read either in Ford's online materials or the digital manual that the underseat battery's primary purpose is alarm related. If in an effort to steal the truck the underhood 12v battery is disconnected to prevent power for the alarm system the underseat battery continues to supply power to sound the alarm. I suspect any alarm equipped version would likely have the same underseat battery pack.

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