Leaving for vacation in Winter - leave FFE plugged in?

I am going to be away on vacation for about 3 weeks in late December and I was wondering whether I should:
1. leave the FFE plugged in:
a. Plus: prevent the battery to get too cold for an extended period of time
b. Minus: usually not good to leave the battery charged at 100% for a long time (it is only good to do it once in a while for maybe a 1-2 days for cell balancing).

2. leave it unplugged at more than 25%, probably around 50-80%?
a. Plus: it is recommended by Ford under normal 70 degF temp, I assume.
b. Minus:
i. Battery stays cold
ii. 12V battery could be drained (Manual recommends to unplug it)

I would like to find out which option is better to not reduce battery life.
Car will stay in a garage. Outside temperatures are between 10-30 degF.
Thanks in advance for your input!

Note: This is what the User manual states:
"LOW AND HIGH VOLTAGE BATTERY STORAGE
If your vehicle is to be stored for 30 days or longer, the high voltage
battery should be charged to above 25% state of charge and the low
voltage (under hood) battery negative terminal should be disconnected.

If your vehicle is to be stored for 3 months or longer, the high voltage
battery should be charged to between 80% and 100% state of charge and
the low voltage (under hood) battery negative terminal should be
disconnected. Failure to do this could damage the batteries.
Note: If battery cables are disconnected, it will be necessary to reset
memory features."

For trips shorter than about 2 weeks I always left my FFE plugged in and set to precondition 2 or 3 times a week. The precondition step turns on the charger and keeps the 12V battery topped up. When I turned my lease in with around 30k miles on the car I really had no noticeable battery degradation.

For longer periods of time I'd do what the manual recommends (leave HV battery slightly discharged, disconnect 12V battery).

The only thing I'd mildly be concerned about would be the 12V battery since there is a constant drain on it. Cold does not harm a stored traction battery, it just diminishes it's capacity while it's cold. Since it's in a garage you could leave the hood up and keep a trickle or float charger on the 12V battery. I did that a couple years ago when I stored the car for about a month and a half, but that was before the software upgrade that supposedly fixed the dead 12V battery issue. Honestly though for 3 weeks I wouldn't worry about it unless you have no way of jump starting it if need be when you get back.

I've left my FFE for several months (4-6 months) on two separate occasions. Both times, the HVB was fully charged on return...but had to jump the 12v battery. I was impressed the HVB held the charge for that long!

A battery tender seems like a good idea. Cheap and easy.

I found this interesting device.
http://www.batterytender.com/future

Although, our vehicle's have this available to us by using MyFordMobile, where we can get alerts when the 12V battery is low.

awefulspeller said:

I've left my FFE for several months (4-6 months) on two separate occasions. Both times, the HVB was fully charged on return...but had to jump the 12v battery. I was impressed the HVB held the charge for that long!

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Ford recommends no more than 30 days sitting without doing anything because the 12v battery has a constant drain keeping the wireless modem alive as well as the keyless entry, etc. Plus lead acid batteries have a fairly high self discharge rate which is why we have float/trickle chargers.

Lithium ion batteries have a significantly lower self discharge rate compared to lead acid batteries. You can leave a Lithium ion battery sit for a year and it's self discharge will be in the low single digit percentage. That is why I used a lithium ion battery for my motorcycle. I never have to put the battery on a trickle charger/battery tender. I'd use one for my car but lithium ion batteries fall flat in the cold making them a poor candidate for a 12v starting battery. The video below is me trying to start my motorcycle in winter to give you an idea why they aren't the best for a starting battery in cold weather.
https://www.youtube.com/watch?v=oHSbL-cBUFM

Normally during winter if we are planning a vacation, we used to store our car in indoor vehicle storage unit. Earlier I used to leave the FFE plugged in overnight during cold temperature to protect the battery.

triangles said:

awefulspeller said:

I'd use one for my car but lithium ion batteries fall flat in the cold making them a poor candidate for a 12v starting battery. The video below is me trying to start my motorcycle in winter to give you an idea why they aren't the best for a starting battery in cold weather.
https://www.youtube.com/watch?v=oHSbL-cBUFM

Click to expand...

Click to expand...

Yeah, but in an EV you don't need to turn over an engine, so the 12v doesn't need huge cranking amps. All that's required is a continuous low amperage draw for the modem etc. and a somewhat higher amp, but momentary, discharge to energized the contactors to connect the traction battery. Once that traction battery is hooked in, the DC-DC converter should power the 12v systems. I'm not sure how many amps are required for the contactors but it can't be that many. A while back I had a 12v that was basically toast (~1 Ah remaining capacity) but it could still start the car just fine as long as it had been topped up with an external charger. The problem was that the small constant loads would quickly drain the battery if the car was off. I seriously doubt this battery would've been able to budge an ICE crankshaft at all.

Amped - you are correct about the contacts for the high voltage battery, it is the highest amperage draw on the 12V battery. When I was having battery trouble, the dashboard and parking lights would all come one. But when I tried to start the car, the high voltage contacts just clicked. It isn't a huge draw, but enough.

And sure enough, there is no way a battery in that state would even close the starter solenoid on an ICE.