Battery Drain When Fully Charged & Still Plugged In

This comes up from time to time, but the short version is when your Leaf is fully charged and still plugged in (L1,L2,ChaDeMo) the 12 Volt battery will experience a "drain" until you unplug your Leaf. While the Leaf is still plugged in, it can't do any "maintenance" charging for the 12 Volt battery to top off the capacity.

I setup an experiment to measure this "vampire" drain and hopefully this information can benefit others in selecting a 12V battery to meet your needs should you need a replacement in the future.

I currently have access to a 2015, 2018, and 2020 Leaf to experiment with. Today, I chose my wife's 2018 :lol: to do this.

To make it more complete, I even put in her original "lead acid" battery for this experiment. I've been keeping it on a maintainer so it goes into her Leaf fully charged already. I charged her Leaf all the way to 100% via our home L2 and then wired it up so I could measure voltage and current while doing another "charge" after the first one was already complete. I expected it to balance the cells for +15 minutes, so I didn't have to wait a long time to begin recording measurements.

Here are the results of this experiment, in summary form.
While charging on the L2, the Leaf is still feeding about (0.073 A x 13.1 V = ) 0.9563 watts into the battery, basically a full 12V battery.

When the Leaf stops charging, DC relays disconnect, all solid blue lights on Dash, the battery begins feeding about (0.638 A x 12.36 V = ) 7.88568 watts back into the Leaf.

After a few minutes, the Leaf goes to sleep and the power drain drops to (0.022 A x 12.3 V = ) 0.2706 watts drain on the battery. I set a timer for 30 minutes and came back a half hour later and the drain was still the same.

Finally after an hour, I disconnected the L2 from the Leaf and noticed a slight drop in power drain. (0.012 A x 12.5 V = ) 0.15 watts

Conclusion: The Leaf uses nearly "twice" as much power while still plugged in versus not. Although this is "twice" as much power, looking at the actual power numbers, a 12V battery would have to be fairly weak to experience a fast death from such a small power load.

This is how much power was going into the 12V battery while it was "charging"


Once charging stopped, you can see power is now being drained from the 12V battery at first.


After a few minutes, the Leaf goes to sleep and the drain becomes much smaller.


After unplugging the L2 from the Leaf, the drain drops a little more.

There is an alleged phenomenon (alleged only because I haven't witnessed it) in which the car periodically verifies that the EVSE is still plugged in, every X minutes. This is supposed to produce a significant additional power drain over longer time frames.

I have no way to compare because I no longer have the older cars, but observations of 12V charging current (in LEAF Spy) convinced me that the 2019 has much lower residual power draw when plugged in after charging complete than the earlier cars. It will be interesting to see if your testing reflects that since you have access to a 2015. I do know that leaving LEAF Spy active on an Android device while the 2019 is parked results in much higher residual power draw regardless if plugged in or not.

LeftieBiker said:

There is an alleged phenomenon (alleged only because I haven't witnessed it) in which the car periodically verifies that the EVSE is still plugged in, every X minutes. This is supposed to produce a significant additional power drain over longer time frames.

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It is in comparison, twice as much power, but the power draws are still very low. This is just one model year, the next one I will test will be the 2015 as part of the Gen 1, might be quite a bit different. :shock:

If your charging cable or adapter is not working properly, it may cause the battery to drain even when it is fully charged. Try using a different charging cable or adapter to see if the problem persists.
contexto

Very interesting thread.
My case - wife's Leaf 2023 model.
traction/high voltage battery at 70%, but using a zappi EV charger. This sends the excess solar energy generated to the car.
It also had a fault on the charger cable (pilot control), which (i think) detected if the car was there or not.
Anyways, the 12v battery kept on being drained (twice so far). The cable has been swapped out, and I have use da 12v smart charger to bring the 12v back to life.
I may plug it in again when the HV battery is lower at 80% and leave it plugged in to see if anything happens to the 12v ...

@knightmb: how are you measuring current draw of the 12V battery? Did you install a monitor that adds a shunt to measure current? I see BT monitors online that measure voltage and current. But I'm leery to insert anything inline with the battery.

BillAinCT said:

@knightmb: how are you measuring current draw of the 12V battery? Did you install a monitor that adds a shunt to measure current? I see BT monitors online that measure voltage and current. But I'm leery to insert anything inline with the battery.

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I did inline for this experiment because I wanted to be able to measure the current flow down to the thousandths place. I do have clamp meters but they are not accurate under 1 amp. Without spending a fortune to get the kind of accuracy I wanted in those types of meters was easy enough to get with an inline setup that already has this built into the meter. This way I could also monitor voltage separately to calculate the power draw. The yellow meter in the pictures is what is measuring the current, it is directly inline, so all power from or to the battery must pass through it first.

knightmb said:

I did inline for this experiment because I wanted to be able to measure the current flow down to the thousandths place. I do have clamp meters but they are not accurate under 1 amp. Without spending a fortune to get the kind of accuracy I wanted in those types of meters was easy enough to get with an inline setup that already has this built into the meter. This way I could also monitor voltage separately to calculate the power draw. The yellow meter in the pictures is what is measuring the current, it is directly inline, so all power from or to the battery must pass through it first.

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Do you have a late model (about the same age) ICE car to compare too? Newest I have is 2000 MY and I will have to see what its loads are, but key off loads have exploded in recent years, it would be nice to have something to compare it too.

cornbinder89 said:

Do you have a late model (about the same age) ICE car to compare too? Newest I have is 2000 MY and I will have to see what its loads are, but key off loads have exploded in recent years, it would be nice to have something to compare it too.

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Long ago, I had plenty (cars, trucks, etc. before selling all of them...) all ICE. The last one to go was my wife's 2004 Volkswagen that got totaled after many years of faithful service. I would be curious myself what vampire power draws exist on more modern ICE. I got plenty of friends and family to experiment on.

What I would want to know for me is if I leave the EVSE plugged in and after it's timer has shut down charging (which it does gracefully through comms they told me), is there still parasitic draw from the nozzle being left plugged in? When I unplug in this state, the LED comes on in the port but I hear no other relays or anything else indicative of a load being turned off. If they are just watching the pilot signal, this I would expect to be done with a low impedance circuit whose drain is (or should be) negligible.

knightmb said:

LI got plenty of friends and family to experiment on.

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Yeah, but Valentines day isn't around again until next year!
I should do the same with my 2000 Camry, just to see what it pulls with the key off. There have been an explosion of key off loads in the last decade or so.
Camry doesn't have any "Onstar" type stuff, and fairly basic in what it "remembers", so I expect a low draw. I don't have anything newer around to test.

cornbinder89 said:

Yeah, but Valentines day isn't around again until next year!
I should do the same with my 2000 Camry, just to see what it pulls with the key off. There have been an explosion of key off loads in the last decade or so.
Camry doesn't have any "Onstar" type stuff, and fairly basic in what it "remembers", so I expect a low draw. I don't have anything newer around to test.

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In my business I've had extensive experience with all manner of DC battery systems (12, 24, 32 & 36vdc) in cars, boats golf cars and RV's. At one time I specialized in installation and maintenance of inverter systems for boats and motorhomes and even did an off-grid system for a friend's large home in Marble, CO.

I've noticed that my wife's 2017 ICE Camry, that we've owned since new, has a relatively substantial parasitic draw on the 12v battery. Since the car has minimal use, with only 28K miles since new, I periodically perform a full overnight slow charge to first bring the battery to 14.4v and then floating at 13.4v for several hours. I've replaced the battery twice. The OEM was replaced at around 40 months when I noticed it dropping below 12v after sitting for a few days after charging. It never had an issue cranking/starting but decided to be proactive and replace it before I had a problem. Bought an Interstate replacement from Costco and noticed after about 18 months that this battery was dropping below 12v after sitting for 10 days after a full overnight charge. Took it back and replaced it under warranty and now the 3rd battery after about 20 months is exhibiting the same behavior. From this I've determined that there is a relatively substantial key-off draw, but have not tested for same to the extent that knightmb in this thread has done on his Leaf.

I've owned 2 Prius hybrids, a Prime PHEV, a Honda Clarity PHEV and 3 Leafs, 2 2022 SV's and a 2023 S, all 40kWh. All of these cars get very light usage and with all of these cars I've noticed that the 12v battery/charging system seems to be a weak link and has issues if not maintained with a supplemental charging of the 12v battery.

Additionally, both of my 2022's had an unexplained one-time, (so far), very rapid key-off discharge of the 12v battery when the cars were less than a year old. Within a matter of hours the 12v battery went from above 12.4vdc to totally dead. Recharging brought the battery back to normal and there has not been a reoccurrence at this time, (several months). I was able to find other 2nd gen Leaf owners online that have experienced the same behavior without any explanation or cause found, even after taking to a dealer for an analysis of the problem.

Needless to say I highly recommend carrying a 12v jump charger to keep from getting stuck or waiting for AAA to show-up to put some 12v to the car to get back up and running.