@waterlubber how did this all work out for you?
Were you successful, and would you mind sharing the steps you ended up using?

I'll be parking my 2011 for about 3.5 weeks this summer and found your question while searching for tips. It seems from your other posts that we are in similar situations in that we both (overpaid) for very low mileage ex fleet vehicles during the height of the post-pandemic used car prices. I got mine with 23,500 kms.

Thanks in advance!

 

I would encourage you to follow the directions above. If your battery is reasonably healthy, it will work. If it is not, it won't.

 

Thank you.

I did see your instructions, and just want to clarify your point on terminating the re-balance early: What SOC should I be looking for at that point? I've noticed after a full re-balance cycle, the SOC sits at about 65%, but how high does forscan take it before it brings it back down to that point?

 

While the Rmode Balance operation is in progress, you can't monitor SoC, but you can definitely hear the transition from the engine being loaded for charging vs. being unloaded and spun by the battery. If you have the nav display and can see the current flow diagram, it will transition from charging to discharging.

I don't recall exactly, but I believe peak SoC during that operation is around 85%. You can check it once you terminate the balance procedure.

65% should be great. The purpose of the disconnects is to ensure that there is no chance of any kind of parasitic draw from the HV battery, and you will only see self-discharge due to that inherent to NiMH chemistry.

I don't remember if I mentioned it, but upon reconnecting and starting, I would allow the car to start and idle charge for 10 minutes or until it self-terminates the charge before driving.

 

@S Keith Thank you!

 

I ended up driving the car up north for the period and thus not storing it overnight. The only procedure I did perform was a test a few days prior, where I allowed the battery to sit for several days and checked the SoC before and after with FORScan. I started with an SOC of 45.98% and finished four days later at 43.98%, with storage at approximately 60-80oF (Florida in October). The battery interlock was removed, but cables and 12V battery left connected. I don't know how SoC is reported; if it's through charge counting, these numbers are useless; if it's through voltage estimation or something else they might actually be useful (and would suggest a useful lifespan of around two months?
Voltage over this period increased from 321.2 V (under 5A load) to 323.18 (under 3A load).

Based on those values, and observing the behavior of the car / preference it for running the engine, I think I could easily last a couple of weeks; the longest I've probably let it sit is a week or so with no issues.

Nonetheless, if you absolutely need to let the car sit, I'd definitely perform the balance, etc. as mentioned above, and prepare to build a backup charger if you need to. To my knowledge, the 2010-11 still have a vestigial connector that make it easier.

 

Unfortunately, SoC comparison isn't a reliable means of tracking self-discharge. SoC is approximated based on temperature, voltage and current. SoC does not change between readings unless current is introduced. Manual charging with the ignition off will not yield a change in SoC either.

This method might yield some value:
Park on day one. Remove safety plug (leave it out).
24 hours later, KEY ON ENGINE OFF.
Record SoC, temperature, pack voltage and del_mod_v value.
X days later, KEY ON ENGINE OFF.
Record SoC (likely identical to prior reading), temperature, pack voltage and del_mod_v value.

Once current is introduced, SoC and voltage comparisons become worthless. It is very important that the HV battery see 0A either way.

Ideally, the temperature will be the same for both readings. Low temp = higher voltage. Higher temp = lower voltage.

Ideally, DEL_MOD_V does not change and remains < 0.19.

The absolute minimum I would be okay with on pack voltage is 308V, which would equate to a low state of charge.

Ending voltage north of 320V, would be in the 40-60% range.