Removing battery for winter storage

[climhazzard]

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.

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!)

Very cool/creative solution. Interesting that your battery is 90ah; mine (US market) is 105ah.

I also hook a 5amp charger up every couple of weeks and have not had the SoC go beyond low 80%s. I do wonder (technically) how the BMS/IBS prevents the battery from hitting 100% via an external charger.

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[roboengr]

Very cool/creative solution. Interesting that your battery is 90ah; mine (US market) is 105ah.

I also hook a 5amp charger up every couple of weeks and have not had the SoC go beyond low 80%s. I do wonder (technically) how the BMS/IBS prevents the battery from hitting 100% via an external charger.

My guess is that once the internal BMS/IBS sensed the battery reaching a desired SoC, it just doesn't draw as much power on the charger to charge the battery anymore (going into "float").

I guess that's why Toyota/BMW states in the manual that the charging must be done through the connection points under the hood rather than popping the trunk and directly hooking it up to the battery so that any external power goes through the vehicle onboard BMS/IBS to avoid overcharging the battery to SoC that's higher than what the OEM software prefers.

 

[climhazzard]

My guess is that once the internal BMS/IBS sensed the battery reaching a desired SoC, it just doesn't draw as much power on the charger to charge the battery anymore (going into "float").

I guess that's why Toyota/BMW states in the manual that the charging must be done through the connection points under the hood rather than popping the trunk and directly hooking it up to the battery so that any external power goes through the vehicle onboard BMS/IBS to avoid overcharging the battery to SoC that's higher than what the OEM software prefers.

Yep, that makes sense, I’m wondering how the IBS actually controls what is being drawn from the battery maintainer. Wouldn’t that require some sort of manipulation to the current between the battery maintainer and battery?

I’m probably getting way off-topic, but it’s a really fascinating subject, and I wish I had more insight into electrical systems.

 

[FRSBRZGT86FAN]

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.

As per the TSB to prevent the moisture you're mentioning:

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