Removing battery for winter storage

[roboengr]

I just bought the car but unfortunately will have to store it away for winter due to salt and snow where I live. The car also park in a condo garage where access to outlet is not possible, so battery tender is out of the question.

I’m thinking to pull the battery out of the car and just charge it and store it in my unit instead.

I’ve searched across reddit and here for winter storage post about pulling the battery out for long term storage (3+ months), but didn’t find anything answering my question.

Has anyone here pulled the 12v AGM battery out for long term storage? I’ve had past issue with other cars where a lack of battery in a car for a long time leads to a bunch of throttle/other ECUs relearning after. I wanted to see if anyone has done this so I know what I’m getting into before I pull it out (especially our supras being a bmw).

Alternatives are buying another cheap 12v battery to swap in every two weeks or so, or buy a LFP power station with built in AC inverter to run a battery tender (essentially using a battery to charge a battery).

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[DR.COKE]

I live in south Florida so i Have no clue about wintering a car. Do you have the option to leave everything alone and start it and let it run in garage to charge the battery and get the engine moving once every 3-4 weeks?
Supra is my weekend car and I’ll have times where I don’t drive it for a month but still start her up just to charge the battery.
if you pull the battery make sure to make a string to pull the hatch open from front door.

 

[climhazzard]

I live in south Florida so i Have no clue about wintering a car. Do you have the option to leave everything alone and start it and let it run in garage to charge the battery and get the engine moving once every 3-4 weeks?
Supra is my weekend car and I’ll have times where I don’t drive it for a month but still start her up just to charge the battery.
if you pull the battery make sure to make a string to pull the hatch open from front door.

Strongly recommend avoiding this practice. Generally speaking, BMW charging logic (“Efficient Dynamics”) does not charge batteries at idle and only does so during deceleration events (there are exceptions if the battery reaches a minimum SOC, but that’s beyond the scope of this post). Running the engine without reaching operating temperature for a period of time creates condensation in the crankcase.

 

[DR.COKE]

Strongly recommend avoiding this practice. Generally speaking, BMW charging logic (“Efficient Dynamics”) does not charge batteries at idle and only does so during deceleration events (there are exceptions if the battery reaches a minimum SOC, but that’s beyond the scope of this post). Running the engine without reaching operating temperature for a period of time creates condensation in the crankcase.

Thanks for tips, I generally run the car idle for 15-30 minutes. More than enough time to heat up engine and cycle coolant several times. comming from Honda, was always taught alternator recharge the battery when engine is running and faster when driving.

 

[climhazzard]

Thanks for tips, I generally run the car idle for 15-30 minutes. More than enough time to heat up engine and cycle coolant several times. comming from Honda, was always taught alternator recharge the battery when engine is running and faster when driving.

Yep, manufacturers have varying approaches. I’m also a former Honda owner; I miss the simplicity of the 51/51R batteries.

 

[roboengr]

I live in south Florida so i Have no clue about wintering a car. Do you have the option to leave everything alone and start it and let it run in garage to charge the battery and get the engine moving once every 3-4 weeks?
Supra is my weekend car and I’ll have times where I don’t drive it for a month but still start her up just to charge the battery.
if you pull the battery make sure to make a string to pull the hatch open from front door.

I would avoid doing that. Starting it up and idling without actually going for a drive will wear out the battery more and causes condensation build up in the drivetrain.

Im leaning towards pulling the battery in this case. The rear hatch issue (where it needs power to prop itself up to unlock) seems to be solvable by attaching a battery/booster to the connection point under the hood when I am ready to hook the battery back up, according to this reddit post.

 

[J29DB03]

Keep in mind power is needed for the window to drop/raise when opening and closing the doors. I really don’t know what happens if it were not be able to move. If you keep the hood unlatched then it’s not something to worry about. Probably best, if possible, would be to put a rag over the latch for the trunk so it can open freely without power.

 

[Vertex]

There are one of two things I would recommend doing if you are storing the car for winter.

First, if it's in a spot and you have access to an outlet I would just throw a maintainer on the car.

If you're unable to use or don't want to purchase a tender/maintainer I would just disconnect the negative cable and have something cover up that post on the battery personally just so you don't have to pull that whole thing out of there or find a spot to store it outside the car. Also, as stated above at the time I wrote this out. I forgot about the windows dropping down some to open the doors, make sure you have the window cracked on the drivers door unless you have it shut while you pull/disconnect the battery and also put something on the liftgate so that it can not close otherwise you're not going to be happy trying to get back into the car again.

 

[RedSupra]

I disconnected the battery and put a rag over the rear latch. I could have hooked up a battery maintainer but I recall something that it should not be hooked up directly to the battery but use the front posts. Any validity to this or is it ok to hook a maintainer up directly to the battery?

 

[Loco38SUP]

Highly recommend this battery tender. Its a better option than disconnecting the battery.

CTEK Battery Tender

-RJM

 

[J29DB03]

I disconnected the battery and put a rag over the rear latch. I could have hooked up a battery maintainer but I recall something that it should not be hooked up directly to the battery but use the front posts. Any validity to this or is it ok to hook a maintainer up directly to the battery?

Correct, recommendation is to use the front, however people have hooked up directly to the battery without any issues. If you’re going to I would say to use one of the tie down bolts for the ground rather than the negative on the battery itself. No idea if it actually makes a difference but it makes sense… to me at least.

 

[roboengr]

FWIW, I came across this document online. It's a TSB from toyota regarding long term storage of Supras.

https://static.nhtsa.gov/odi/tsbs/2020/MC-10174897-9999.pdf

 

[bk5]

You could use a Jackery to trickle charge the car without access to an outlet. Even a small one will run a trickle charger for several hours. The might even make battery powered jump packs that can trickle charge, but I've never looked.

Doing this once every two-three weeks will be plenty. I don't leave mine on a dedicated trickle charger in the winter, I just pop it on a few times over the winter and have never seen the voltage drop.

 

[roboengr]

You could use a Jackery to trickle charge the car without access to an outlet. Even a small one will run a trickle charger for several hours. The might even make battery powered jump packs that can trickle charge, but I've never looked.

Doing this once every two-three weeks will be plenty. I don't leave mine on a dedicated trickle charger in the winter, I just pop it on a few times over the winter and have never seen the voltage drop.

With other fellow members pointing out the windows lowering require power as well as hatch access, I've decided to buy a power station to run a charger/maintainer every few weeks to charge up the car from the connection under the hood.

 

[roboengr]

Update on my final solution. Hopefully useful for future poor souls who also live in a condo/apartment without access to a plug and need to store the car and maintain their battery.

Going with the "using a portable battery to run a battery tender to charge my supra" route.
Here's my setup:

• EcoFlow River 2 Portable Power Station (Got it for $179 CAD during the holiday sale)
• Battery Tender 5Amp Charger/Maintainer (Got it for free from my friend who no longer has use for it)

The River 2 has an advertised 256wh capacity. Some back-of-napkin calculation tells me (12v*5amps = 60w) that this should be good for running my battery tender at 5amp (charging) for around 3-ish hours, considering there are losses between conversions.

Real-world testing shows around 2.5-3 hours and for some reason, the wattage readout from the battery tells me it's drawing around 80w instead. (EDIT: Given charging occurs at 14v+, 80w would make sense for 14.4v @ 5a with spare changes for sensing/measurement error)

Running the charger for 2.5 hours raised the battery state-of-charge (SOC) by around 10% (mine went from around 65% to 75% through bimmerlink, with the original 90ah bmw battery).

Based on this, I will probably do a charge every 2 weeks or so once I get the SOC high enough. (I've heard the vehicle doesn't charge beyond 80% due to inherent bmw's battery management design, we will see!)

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