Key-off battery drain

I have not seen this topic addressed, but apologies if this is oft-covered ground.

I understand that the Leaf draws current from its 12 volt battery to power lights and accessories--including, I assume, those systems that need constant current during off mode--computer memory, anti-theft monitoring, clocks, etc.

I also understand that the PbAc battery is recharged by the LI battery. What i can't seem to find is just how and when this is done.

EV wisdom says don't leave the car at 100% charge for "very long." But wouldn't the normal PbAc battery drain as I described above reduce the charge level on the LI battery anyway?

The 12V battery is charged by a DC-DC converter inside the car. This only runs under certain circumstances and I don't really know the details.

The 12V capacity and use is very small compared to what the main Li battery stores so it doesn't have any significant effect on the amount of charge in the Li battery, at least in the time frame of hours. Over the course of days, the 12V battery could pull a few % of charge from the main battery (assuming the car charged it....) but there is no good reason that I can think of to do that.

The car periodically turns on the DC-DC converter to charge the 12-volt battery from the traction battery while parked. The residual current draw on the 12-volt battery is quite low when the car is parked so there is very little drop in SOC (state of charge) level of the traction battery even when parked for a month. I always make sure the traction battery is not over 70% SOC when parking for extended time.

Thank you!

There are actually many topics on the 12 volt battery, and most of them include a description of how the sometimes-inadequate charging algorithm of the Leaf (especially the earlier years) works - and when it doesn't, like when the car is plugged in but not charging.

ULYLeaf said:

EV wisdom says don't leave the car at 100% charge for "very long." But wouldn't the normal PbAc battery drain as I described above reduce the charge level on the LI battery anyway?

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As mentioned, it is a small drop on the Li-ion battery level over a short period.

Here is my experience, as an example:
I went on vacation in August last year and left my Leaf stored in the garage for 21 days, unplugged, w/o 12V-battery trickle charger.
Li-ion battery level as-left: 87%
Li-ion battery level as-found: 77%

So, I was looking at a 10% drop in the Li-ion battery level after 21 days.

henrydehoja said:

ULYLeaf said:

EV wisdom says don't leave the car at 100% charge for "very long." But wouldn't the normal PbAc battery drain as I described above reduce the charge level on the LI battery anyway?

Click to expand...

As mentioned, it is a small drop on the Li-ion battery level over a short period.

Here is my experience, as an example:
I went on vacation in August last year and left my Leaf stored in the garage for 21 days, unplugged, w/o 12V-battery trickle charger.
Li-ion battery level as-left: 87%
Li-ion battery level as-found: 77%

So, I was looking at a 10% drop in the Li-ion battery level after 21 days.

Click to expand...

That is much more loss of charge than I typically have. Did you leave something plugged in to the OBDII port? I typically see either the same SOC or 1% to 3% loss of charge when I return to the car after as much as a month.

GerryAZ said:

That is much more loss of charge than I typically have. Did you leave something plugged in to the OBDII port? I typically see either the same SOC or 1% to 3% loss of charge when I return to the car after as much as a month.

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Nothing was in the OBDII port. Aside from a USB charger (no-light type) left in the power port with just a cable connected to it, nothing that I saw was connected or left ON.
I'm not sure if the summer heat had anything to do with it. There was construction going on in the house during that time, for a kitchen renovation, and the contractor may have used the garage for extra work space.
That was my first time leaving it alone for such a long time.

The typical standby/sleep-mode Leaf 12V battery current drain should be about 50/60 ma (milliamps). This occurs a few minutes after the
Leaf is locked. Using LeafSpy should provide you an insight as to when the 12V battery is being charged, i.e. a voltage greater than 12.5-13.0.

GerryAZ said:

...I typically see either the same SOC or 1% to 3% loss of charge when I return to the car after as much as a month.

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This is my experience as well.

GerryAZ said:

That is much more loss of charge than I typically have. Did you leave something plugged in to the OBDII port? I typically see either the same SOC or 1% to 3% loss of charge when I return to the car after as much as a month.

Click to expand...

Is that what you see on your 2019 model?

Nubo said:

GerryAZ said:

...I typically see either the same SOC or 1% to 3% loss of charge when I return to the car after as much as a month.

Click to expand...

This is my experience as well.

Click to expand...

Is that what you see on your 2018/2019 model?

henrydehoja said:

Nubo said:

GerryAZ said:

...I typically see either the same SOC or 1% to 3% loss of charge when I return to the car after as much as a month.

Click to expand...

This is my experience as well.

Click to expand...

Is that what you see on your 2018/2019 model?

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No, with a 2012 and 2015.

For those that are interested in the energy consumed by a 50ma standby current drain on the 12 volt battery over one month:

Energy (12V battery) = .05 amps X 12V X 24 hrs X 30 days = 432 Whrs = .43 kWhrs

Assuming 80% conversion efficiency on the converter, the load energy loss on the main battery is about .5 kWhrs.
For a 24 kWh battery in one month, that's about 2% loss.

@ Henry,

i would guess that your USB chargger has an internal power supply that is always ON, even if nothing is plugged on the cable, and that accounts for your higher drop in SOC. The 12V aux battery was being drained at higher than nominal, and the DC-DC was operating more frequently and using energy from the pack.

+1 on the good analysis by loren

It's also becoming clear that the 2018+ Leaf is only slightly better at keeping the 12 volt battery charged, so if the car "forgets" to top it off with a phantom drain, or if the period between top-offs is too long to compensate for the drain, the 12 volt battery has less reserve capacity available to keep everything working properly. IOW you're almost as likely to see a 12 volt battery failure as you are with earlier Leafs.

As mentioned, it looks like the USB charger (Aukey CC-S1) was a significant parasite.

I rigged up some batteries to get 12 Vdc, hooked up my multimeter inline with the batteries & USB charger, and measured a current draw of 0.169A on the input side of the unloaded charger (w/ or w/o the USB cable).

Using lorenfb's method, for this USB charger:
Energy (12V battery) = 0.169A X 12V X 24hrs X 21days = 1022.11 Wh = 1.02 kWh
Assuming 80% efficiency on the converter, the load energy loss on the main battery = 1.02 kWh / 0.8 = 1.28 kWh
For my 40 kWh battery, that's about a 3.2 % loss.

henrydehoja said:

GerryAZ said:

That is much more loss of charge than I typically have. Did you leave something plugged in to the OBDII port? I typically see either the same SOC or 1% to 3% loss of charge when I return to the car after as much as a month.

Click to expand...

Is that what you see on your 2019 model?

Click to expand...

The SOC same or 1% to 3% loss is what I saw for both the 2011 and 2015. The 2019 has only been parked long term a couple of times, but so far the SOC has stayed about the same.