Possible "backup solution" for failed 12-volt battery??

[T1328]

Since I got my first EV (they pretty much all have this 12V battery dying issue to various degrees, I've had one of these Die Hard jump starters around. Isn't the Mach-E's frunk able to be opened manually by double pulling on the handle that is usually used to open the hood of normal cars, allowing you to use one of these? https://a.co/d/5z4gFPL

I live my life creating backup solutions to problems I haven’t had as my working career was in business continuity and of course it drives my family crazy. I’ve not had a 12-volt battery problem yet with my 12-month-old MME but I was thinking of a relatively inexpensive way to ensure you could always get in your car, at a minimum, if your 12-volt battery drops out of the working world and assume it's at the worst possible time which varies by your level of paranoia. So, with too much time on my hands, and little electrical engineering knowledge I was thinking perhaps by using identical MME 12V batteries, wire them in parallel, and put a Remote Controlled Disconnect Switch (below) between the 1st (primary) and 2nd (backup) and have the normal position of the 2nd battery as not connected. Then, theoretically, if a failure of the primary 12v battery occurs and you cannot open the frunk, you can use the remote (if you have it with you) to connect the 2nd battery into the parallel wiring. Theoretically that should allow the 12v backup battery to provide power as normal. You could add an A/B switch, like boats use, in between the Primary and Backup so when you got the frunk open you could take the primary battery out of the wiring configuration altogether. I know you would have to keep the backup battery charged with a trickle charger/etc. but what has my lack of knowledge missed here?

Amazon.com: 250A Remote Battery Disconnect Switch 12V Upgraded Battery Kill Switch for Car RV Truck Camper Dual Remote Control Anti-Theft Battery Shut Off Switch Prevent Battery Drain (450A Starting Current) : Automotive

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[Doobster6]

I live my life creating backup solutions to problems I haven’t had as my working career was in business continuity and of course it drives my family crazy. I’ve not had a 12-volt battery problem yet with my 12-month-old MME but I was thinking of a relatively inexpensive way to ensure you could always get in your car, at a minimum, if your 12-volt battery drops out of the working world and assume it's at the worst possible time which varies by your level of paranoia. So, with too much time on my hands, and little electrical engineering knowledge I was thinking perhaps by using identical MME 12V batteries, wire them in parallel, and put a Remote Controlled Disconnect Switch (below) between the 1st (primary) and 2nd (backup) and have the normal position of the 2nd battery as not connected. Then, theoretically, if a failure of the primary 12v battery occurs and you cannot open the frunk, you can use the remote (if you have it with you) to connect the 2nd battery into the parallel wiring. Theoretically that should allow the 12v backup battery to provide power as normal. You could add an A/B switch, like boats use, in between the Primary and Backup so when you got the frunk open you could take the primary battery out of the wiring configuration altogether. I know you would have to keep the backup battery charged with a trickle charger/etc. but what has my lack of knowledge missed here?

Amazon.com: 250A Remote Battery Disconnect Switch 12V Upgraded Battery Kill Switch for Car RV Truck Camper Dual Remote Control Anti-Theft Battery Shut Off Switch Prevent Battery Drain (450A Starting Current) : Automotive

A good idea. I especially like the ‘boat-like-switch’ idea to allow easy substitution of the secondary battery! Seriously; like on my boat, lift a cover and rotate the switch to the secondary battery and off you go!
All that said, this whole issue illuminates what a horrible engineering job Ford did with this whole system. They should have never offered us an alternative to ICE vehicles that introduces stupid new problems like: a) not being able to even get into your car, or open the frunk-lid, if the tiny 12V battery fails, and b) the ridiculous Rube-Goldberg regimen required to respond to problem ‘a’. They couldn’t even include a hinged lid under the hood to make accessing the 12V battery easier; this at least should have been included in the 2025 update along with the heat pump, since they obviously had to rework the plastic frunk to fit the pump paraphernalia.
Seriously, if they can’t resolve the problem with ‘proper’ engineering, then give us the secondary battery, and an easier way to open the frunk to get to the switch (assuming that’s where they put it!).

 

[nlions]

Since I got my first EV (they pretty much all have this 12V battery dying issue to various degrees, I've had one of these Die Hard jump starters around. Isn't the Mach-E's frunk able to be opened manually by double pulling on the handle that is usually used to open the hood of normal cars, allowing you to use one of these? https://a.co/d/5z4gFPL

My hypothetical was "worst case" which includes 12 volt battery is dead, being locked out of car (FOB and keypad on pillar don't work) and without a 12 volt source to use for the external frunk connection.

 

[MadMatt]

On this note,

I've recently been monitoring my 12v status with a obd2 scanner and surprised to see the car never lets it get under 85% SoC.

I remember reading the original Ford programming was allowing it to get as low as 40% before charging it back up.

I'm assuming they completely changed how the 12 battery is handled on new Mach E's (mine being a 2024 LFP).

 

[Smoke & Bells]

As a mathematician and retired engineer there are 2 solutions to solve this problem of being locked out of a car by a dead battery.
1. Have a keyed door or trunk as a option when buying the car (simple) ?
2. Carry a 12 volt battery and jumper cables in your backpack (hard) ! ?

 

[superdave80]

I would keep a jump pack in the frunk

Yes, and then you can use the jump pack to open... the... frunk?

 

[Deleted member 26087]

So you’ll have 2 batteries that fail in 3 years instead of one? Brilliant!

?

 

[Phantom E]

I think the string method is the cheapest and most reliable.

 

[Snakebitten]

The @markboris mod is so inexpensive and sensible. I'm a little bit like the OP and a hostage to my brain's delight of imagining all kinds of solutions. It's thoroughly enjoyable, to be honest.

But most times reason wins out and I land on more solid ground.

Being able to get some recovery current from external the interior or the Frunk is a great approach for a "what if"

 

[MTNestr]

I have an additional 12v battery under my seat to power my dashcam. Could you wire a remote controlled relay to supply power to the cables in the front bumper which opens the frunk?

 

[FrankM1]

I am working on a plan that uses a jump starter (from my former ICE car) that has a 20 Ampere output. A connector will be used at the 12-volt output that will be fed to a key switch. The switch will control the power that will be routed to the emergency jump start circuit either directly or by plugging it in to a socket at the front access door. I may connect it to the battery as an alternate. A 20 Amp. fuse will also be installed. I am trying to determine the best place for the switch. I had considered the charging port area since it has weather protection but, there isn’t enough room there. I may have to get a better switch to handle all weather conditions if it’s on the body.

 

[moog]

All our FOBS have keys in them. Could have keyed them (you know like pretty much all cars), and had a mechanical lock at the trunk.

Open trunk, pull wire in a side panel, opens back door.

Simple easy.....but it cost $$$.



I also think Ford had too much TESLA design in their heads at the time. The whole "we are too cool and advanced for keys. The whole NO key, Use your Phone, use the keypad.

They spent so much time and $$ on that R&D, that they had no $$ left for a "what if" simple mechanical solution.


Now we get "locked out of car.....in the middle of nowhere....with no 12V source around to open the frunk.....and you can't even get inside the car!!!!!

 

[bbulkow]

Some people have had the battery fail in a state where it doesn’t have enough power to unlock the car, but still has enough voltage to inhibit the frunk jump.

But.... those were bugs.... and ford has pushed out a lot of changes.

Do we have cases that the "living dead state" is happening to fully updated cars at the moment?

That there are cars that "brick" and won't be opened by 12v to the frunk points?

 

[Maquis]

But.... those were bugs.... and ford has pushed out a lot of changes.

Do we have cases that the "living dead state" is happening to fully updated cars at the moment?

That there are cars that "brick" and won't be opened by 12v to the frunk points?

I can’t prove or disprove that. I don’t think we know.

 

[bbulkow]

As a mathematician and retired engineer there are 2 solutions to solve this problem of being locked out of a car by a dead battery.
1. Have a keyed door or trunk as a option when buying the car (simple) ?
2. Carry a 12 volt battery and jumper cables in your backpack (hard) ! ?

Google "window hammer tool", this trivially allows breaking the window. The front doors are mechanical, two pulls. Lighter than a 12v battery. Just in case you're stuck in a location with no pointy rocks. Gets you into a car if you're locked out, no problem.

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