Al123
Posts: 4
Joined: Sun Nov 17, 2019 5:07 pm

Storing a Mitsubishi I-Miev outside during the winter

Sun Nov 17, 2019 6:01 pm

I have recently bought a 2012 I-Miev. The car is badly rusted. I have decided not to use it in the winter. I am in Ontario, and it can get cold in the winter. I have noticed, that the main battery doesn't have any noticeable discharge with the car parked. The 12V battery when disconnected, also discharges only minimally.
A top up once a month would do.
But when the 12V battery is connected, it discharges faster, and I would have to charge the 12V battery once a week. It likely keeps the computer memory. I don't care about that.
My first plan was to discharge the main battery to 40%, and disconnect and charge the 12V battery.
And check the status of the main battery once a month, and top it up to 40% if needed.
Then I have found about the main battery using a heater to heat itself when it is colder than -25C. Does it do it when the car is off?
Would it do it when 12V battery is disconnected? How bad would it be not having this feature? It can get to -25 degrees C at night, but maybe only 10 times in the winter. Most of the time it is -5 to -20 degrees C.
Thank you for your reply.

Don
Site Moderator
Posts: 2901
Joined: Thu May 10, 2012 3:55 pm
Location: Biloxi MS

Re: Storing a Mitsubishi I-Miev outside during the winter

Tue Nov 19, 2019 9:05 am

Al123 wrote: . . . . I have found about the main battery using a heater to heat itself when it is colder than -25C. Does it do it when the car is off?
Would it do it when 12V battery is disconnected?

Thankfully, I've had no need to research what protections the car might employ to keep the traction battery from freezing in the conditions you mentioned, but I'm 99% sure there would be none of them implemented if the 12 volt battery is disconnected - Without 12 volts present, everything in the car is effectively 'dead' - It's temperature sensing circuitry needs 12 volts to function

I stored one of our cars for about 10 months with the traction battery at about 35%, occasionally starting it, but never in the conditions you're talking about. When it came time to drive the car again, I had to first replace the 12 volt battery. If I had it to do again, I would leave a trickle charger connected to it 24/7, but . . . . if I was leaving it outside in -25C temperatures, I would bring the 12 volt battery inside - It's a standard lead acid battery and I think it might freeze, even with a trickle charger on it

Don
2012 iMiEV SE Premium, White
2012 iMiEV SE, White
2017 Chevy Volt Premier
2014 Ford Transit Connect XLT SWB wagon, 14,000 miles
1979 Honda CBX six into six

Al123
Posts: 4
Joined: Sun Nov 17, 2019 5:07 pm

Re: Storing a Mitsubishi I-Miev outside during the winter

Tue Nov 19, 2019 4:16 pm

The owner manual says, that to charge the 12V battery, it has to be disconnected from the car.
My solution is to disconnect only the negative terminal, and charge the battery in the car. (leaving the positive terminal connected).
I just make sure, that my charger, which is grounded doesn’t touch the body of the car.
It works well.
The reason I have disconnected the negative instead of the positive is because the negative terminal is in the open, and has only one wire attached to it. The positive terminal has many wires attached to it.
In my case, the 12V battery is new, replaced by the previous owner, who didn’t charge the original 12V battery, and it has gone bad.
It is not too cold here yet, so I have the negative cable disconnected from the 12V battery.
The 12V battery is fine in the cold temperature. It will not freeze.

DBMandrake
Posts: 219
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: Storing a Mitsubishi I-Miev outside during the winter

Mon Nov 25, 2019 2:52 am

If it was me I would discharge the traction battery to about 50% and connect an intelligent 12v battery charger/conditioner that has an automatic maintenance/trickle mode to the 12v battery while it is still connected to the car, and leave it connected.

Owners manuals always say don't connect a charger to the battery while it's in the car but that's just to cover themselves in the event that the charger was faulty and subjected the electronics in the car to excessively high voltage (above about 15 volts) however the chances of that happening with a modern intelligent computer controlled charger are basically zero, if anything they are smarter than the relatively "dumb" charger in the car itself.

If you leave the 12v battery disconnected for a few months the BMU will (apparently) lose all record of the state of health of the traction battery - I would definitely try to avoid this as it could take a long time for it to re-learn the SoH of the battery without a diagnostic session to perform a battery capacity measurement. If the SoH figure for the battery is drastically in error that means you will either run out of charge very suddenly when you think you have a lot of range left, or not be able to drive as far as you should, depending on which way the error is.

As long as it remains fully topped up, a 12v lead acid battery will not freeze until -70C.

One possible issue of leaving the car outside in -25C conditions for a long time is that the electronics of the 12v charger itself may have difficulties operating in those extremely low temperatures unless the idle power it consumes is enough keep itself warm. You might actually want to wrap up the charger and put it inside the car or under the bonnet - don't leave it exposed to the elements even if it's water proof...
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

Return to “Batteries and Battery Management”