If you've had issues with the 12V battery in your leaf failing prematurely, go out and unplug the low voltage connector on the negative terminal.

[LeafNissan1]

I have posted in previous threads on this forum dealing with 12v battery issues relating my experiences with 3 of my gen 2 Leafs as well as with 12v issues I experienced with my Toyota and Honda PHEV's, all of which have used dc to dc charging rather than a traditional alternator.

I found mcmancuso's tip, about disconnecting the 4-wire plug on the negative battery terminal, to work exactly as he described. That is the dc to dc charging outputs and keeps the battery charging at a constant 14v, as long as it's on, as is similar to the way an alternator on an ICE vehicle functions.

The only negative is that I noticed a slight decrease in my m/kWh, (.1—.2), which, as a hyper-miler, I monitor very closely. This makes sense, as obviously maintaining the 12v battery at a constant 14v is going to pull some energy from the traction battery.

I have a 12v bluetooth monitor connected to the battery along with a pigtail connected directly to the battery terminals, that gives me the ability to monitor and connect a charger w/o opening the hood. I connect my charger whenever the battery drops below 12.35v, which is about once a week. I leave the charger on overnight, so that the battery charges up to 14.2v and then floats at 13.4v until I remove it the following day. I only drive this car once or twice a week, about 200—250 miles per month.

So if you don't want to go through this hassle, then definitely disconnect the plug from the negative terminal like mcmancuso recommends, as a good way to maintain the 12v battery. However, with this method, I wouldn't let the car sit for more than 10 days to 2 weeks without fully charging the 12v battery.

 

[mcmancuso]

My 2012 requires a new battery about every 3 years. My 2012 Tesla S Lithium ion 12V's last about 5 years. Batteries in my ICE vehicles last as long as 20, even if weeks elapse between drives. The Leaf battery is happiest when daily driving keeps it topped off. If I'm going out of town for an extended period, I usually disconnect the battery (I replaced the nut that holds the power cable to the post clamp with a wing nut so it is very easy to disconnect, and I can leave the post clamp itself clamped on the battery post.) But this means that I lose some of the settings (like charging limit set to 70%).

If I'm not planning to drive in the next 72 hours I connect a trickle charger/desulfator to the battery. But battery life is still suboptimal, even with these hacks.

I do wonder how much power is consumed by the TCU (which is now essentially worthless due to no cellular connection) and have considered unplugging it, but I don't know whether any other systems would be affected.

If you just unplug the TCU itself nothing else is affected, I unplugged the one in my 2013 without issue after the 3G network cutoff.

 

[LeafNissan1]

"I do wonder how much power is consumed by the TCU (which is now essentially worthless due to no cellular connection) and have considered unplugging it, but I don't know whether any other systems would be affected."

This video may be of interest on the amount of parasitic draw on the 12v Leaf batteries:

 

[mcmancuso]

However, with this method, I wouldn't let the car sit for more than 10 days to 2 weeks without fully charging the 12v battery.

That's going to be the case regardless of the mod here, as this has no effect on the car's charging behavior when it's sitting (and not actively charging or being driven).

 

[MK1]

I have posted in previous threads on this forum dealing with 12v battery issues relating my experiences with 3 of my gen 2 Leafs as well as with 12v issues I experienced with my Toyota and Honda PHEV's, all of which have used dc to dc charging rather than a traditional alternator.

I found mcmancuso's tip, about disconnecting the 4-wire plug on the negative battery terminal, to work exactly as he described. That is the dc to dc charging outputs and keeps the battery charging at a constant 14v, as long as it's on, as is similar to the way an alternator on an ICE vehicle functions.

The only negative is that I noticed a slight decrease in my m/kWh, (.1—.2), which, as a hyper-miler, I monitor very closely. This makes sense, as obviously maintaining the 12v battery at a constant 14v is going to pull some energy from the traction battery.

I have a 12v bluetooth monitor connected to the battery along with a pigtail connected directly to the battery terminals, that gives me the ability to monitor and connect a charger w/o opening the hood. I connect my charger whenever the battery drops below 12.35v, which is about once a week. I leave the charger on overnight, so that the battery charges up to 14.2v and then floats at 13.4v until I remove it the following day. I only drive this car once or twice a week, about 200—250 miles per month.

So if you don't want to go through this hassle, then definitely disconnect the plug from the negative terminal like mcmancuso recommends, as a good way to maintain the 12v battery. However, with this method, I wouldn't let the car sit for more than 10 days to 2 weeks without fully charging the 12v battery.

Any chance you could please post a photo of the charging cable location/how it looks when you charge the 12v without having to open the hood? Did you have to drill through the plastic next to the main charge points for the cable to reach? Thanks.

 

[LeafNissan1]

Any chance you could please post a photo of the charging cable location/how it looks when you charge the 12v without having to open the hood? Did you have to drill through the plastic next to the main charge points for the cable to reach? Thanks.

This type of plug/pigtail comes with BatteryTender brand chargers or can be purchased separately. It's flat and can be slid out to connect and slid back in to be all but unnoticeable when not in use. There is just enough room between the hood and the headlight clear plastic on 2nd gen Leafs when the hood is closed. No modification necessary, just attach other end to positive and negative battery terminals, you can install an inline fuse if it makes you feel more comfortable, I didn't worry about this.

 

[MK1]

This type of plug/pigtail comes with BatteryTender brand chargers or can be purchased separately. It's flat and can be slid out to connect and slid back in to be all but unnoticeable when not in use. There is just enough room between the hood and the headlight clear plastic on 2nd gen Leafs when the hood is closed. No modification necessary, just attach other end to positive and negative battery terminals, you can install an inline fuse if it makes you feel more comfortable, I didn't worry about this.

View attachment 4753
View attachment 4754
View attachment 4755

Thank you very much for getting back and sharing this on the forum. This is good to know and looks like a great solution if using a 12v charger often.

 

[LeafNissan1]

Thank you very much for getting back and sharing this on the forum. This is good to know and looks like a great solution if using a 12v charger often.

You are very welcome, my pleasure, have a great weekend.

BTW, this is the bluetooth battery monitor I also installed, I found out about this product on this forum from another contributor. https://www.amazon.com/dp/B07GP1RXYZ?psc=1&ref=ppx_yo2ov_dt_b_product_details

 

[corkycal]

Are you only using the battery tender when you’re not using the leaf for an extended period? If you’re driving normally, there’s no need for this?

Or you’re plugging this in daily just to top off the battery to full capacity daily?

 

[BillAinCT]

This battery monitor is the same and is a couple of bucks less and may arrive a day sooner.

 

[corkycal]

I have posted in previous threads on this forum dealing with 12v battery issues relating my experiences with 3 of my gen 2 Leafs as well as with 12v issues I experienced with my Toyota and Honda PHEV's, all of which have used dc to dc charging rather than a traditional alternator.

I found mcmancuso's tip, about disconnecting the 4-wire plug on the negative battery terminal, to work exactly as he described. That is the dc to dc charging outputs and keeps the battery charging at a constant 14v, as long as it's on, as is similar to the way an alternator on an ICE vehicle functions.

The only negative is that I noticed a slight decrease in my m/kWh, (.1—.2), which, as a hyper-miler, I monitor very closely. This makes sense, as obviously maintaining the 12v battery at a constant 14v is going to pull some energy from the traction battery.

I have a 12v bluetooth monitor connected to the battery along with a pigtail connected directly to the battery terminals, that gives me the ability to monitor and connect a charger w/o opening the hood. I connect my charger whenever the battery drops below 12.35v, which is about once a week. I leave the charger on overnight, so that the battery charges up to 14.2v and then floats at 13.4v until I remove it the following day. I only drive this car once or twice a week, about 200—250 miles per month.

So if you don't want to go through this hassle, then definitely disconnect the plug from the negative terminal like mcmancuso recommends, as a good way to maintain the 12v battery. However, with this method, I wouldn't let the car sit for more than 10 days to 2 weeks without fully charging the 12v battery.

Thanks for sharing this info. From reading your thread, you did not disconnect the plug (TCU?) from the negative terminal because it affected your milage. You added the Bluetooth battery monitoring system onto your battery to monitor the voltage. You added the battery tender plug so it’s easier to top off the battery if it falls below 12.5v. This is your way to preserve your battery for longer than the typical 3 years? Maybe it will preserve for 5 years like on ICE cars???

 

[LeafNissan1]

Are you only using the battery tender when you’re not using the leaf for an extended period? If you’re driving normally, there’s no need for this?

Or you’re plugging this in daily just to top off the battery to full capacity daily?

I use the battery tender about once a week. Usually plug it in for a couple of hours until, but only after, it goes into float. The little tender that I use is the Battery Tender brand which is rated at 750mah. I also have a couple the Battery Tender 3ah smart chargers that Costco used to sell periodically at a $10 discount for $29.99 and it came with a variety of connectors. From the old days I have a couple of Schauer brand ferroresonate 15amp chargers, that if I'm in a hurry or have a dead battery, I use. I can get one of those chargers to bring a battery up above 15vdc, should I want to deliberately overcharge to equalize the cells.

I only use my Leaf about once or twice a week (50 miles) and charge at home, most of the time at Level 1. I've had a lifetime of experience dealing with all manner of batteries and now that I'm an old geezer with too much time on my hands, I spend way more of it on this than is necessary. So, as I posted earlier, if you don't want to go through this hassle, use mcmancuso's tip. Your battery will be better maintained and the only negative that I see is a slight decrease in your m/kWh.

 

[LeafNissan1]

Thanks for sharing this info. From reading your thread, you did not disconnect the plug (TCU?) from the negative terminal because it affected your milage. You added the Bluetooth battery monitoring system onto your battery to monitor the voltage. You added the battery tender plug so it’s easier to top off the battery if it falls below 12.5v. This is your way to preserve your battery for longer than the typical 3 years? Maybe it will preserve for 5 years like on ICE cars???

 

[LeafNissan1]

All of that is correct except I did disconnect the plug from the negative terminal and tested it to see the affect and I said if it drops below 12.35v not 12.5, which is just my arbitrary low voltage level.

Yes, I believe that by maintaining the battery with a battery tender you could likely get up to 5 years on an OEM equivalent 12v battery. But be sure to always carry a 12v backup source with you to connect should you get stuck.

The OEM in my 2022 Leaf will hit 3 years in January of 2025, so will do a load test on it again before it goes out of warranty. Depending on the outcome, I'll try to get Nissan to replace it should it fail the load test. If it's still good at that time, when I do replace it, I'll buy the 51r at Costco for $124.99, which has a 3 year full replacement warranty and should I keep the car long enough, just swap it out every 3 years while still under warranty.

BTW I did consider and research using a LiFeO4 battery like knightmb recommends and promotes and found one on sale for $149.99 (Ohmmu) on evannex.com specifically sold as a replacement for the Leaf. And another one recently on Amazon for $135. With the Amazon one you need to buy JIS to SAE adapters and may have to modify the hold-down bracket. Be advised that the BMS on those batteries that I found that are sold on Amazon is not specifically designed for automotive use, not sure about the Ohmmu brand, however this does not necessarily mean they won't work.

 

[corkycal]

Thank you for all your research on this topic!

My 2019 battery failed the load test from the dealer and they suggested replacing. I removed the plug from the negative terminal and everything is working fine. I know my battery is due for a change since it’s 5 years old.

I’ll go the Costco route for a 51R battery and buy a battery tender and Bluetooth battery monitor as suggested.

 

[NoahJ]

So I am wondering if the battery drain issue on my 2013 leaf is due to the cellular system and it never having signal because the device is too old to communicate with newer cellular towers. Would it harm anything to remove the cellular card in the vehicle?

 

[LeafNissan1]

Thank you for all your research on this topic!

My 2019 battery failed the load test from the dealer and they suggested replacing. I removed the plug from the negative terminal and everything is working fine. I know my battery is due for a change since it’s 5 years old.

I’ll go the Costco route for a 51R battery and buy a battery tender and Bluetooth battery monitor as suggested.

You're welcome and thanks for relaying your experience with your OEM 12v battery.

 

[CHLPatent]

After 2 failed batteries, I got a voltage/SoC monitor for the 12V battery and logged several months of data from it.

Initially in it's factory configuration, I saw a constant decrease in the battery charge state with brief periods of appropriate charging, but never enough to top it back off.

I found a discussion regarding the negative terminal current monitor, how the LEAF uses information from that monitor to control the charge going to the 12V battery, and that disconnecting it will cause the LEAF to put the maximum charge voltage to the battery whenever it's in a charging state (this is fine for lead-acid batteries, and is similar to how they charge in a gas vehicle with an alternator that puts out a constant voltage).

Sure enough, disconnecting that plug and leaving it off is now allowing the car to fully charge the battery, and I've had zero issue with it since then.

I've found all of my issues with the 12V battery have gone away after I disconnected this plug (4 wire black connector on the negative terminal) under the hood (this is the connection for the current monitor). This is applicable for 2013 MY and newer Leafs.

--------

Interesting.

After I initially got my 2012 Leaf in Dec 2011, I took a long vacation and when I came back, the 12v was dead.

After jumping it I read that turning off the charge timer in the menu made a big difference in the amount of 12v battery drain.

Just to be safe and to extend battery life, I bought a battery maintainer.

I am still on that original battery almost 12 years later.

On a somewhat related topic about a different EV, my 2023 Ford F-150 Lightning has 12v battery issues and many other owners on the forums are reporting the same or related issues.

The over the air (OTA) updates will not install if the 12v battery is not at an adequate SOC, apparently 85% or so.
There is a DC-DC circuit that will transfer energy to the 12v from the Li battery (HVB) when the battery reaches a certain discharge level, but it is set at 40%. The batteries are AGM so going below 50% is not a good idea for battery life - go figure.
The 12v also charges from the HVB when the vehicle is being driven or in drive-ready mode (turned on).
But if you don't drive frequently, the 12v discharges pretty quickly due to all the vampire electronics running even when the truck is off.

There is the capability written into the battery management system (BMS) for the 12v battery to top it off before installing an OTA update.
But apparently that procedure has not been utilized by Ford's OTA software updates.
So many people have not been able to install OTA updates.
I had to turn my truck on in drive ready mode, turn off everything possible that used 12v battery power, lock the truck and let it sit for close to 8 hours like that before the battery was charged enough to install an update.

Also, some people have replaced their AGM battery after less than the 3 years of bumper to bumper warranty.
Some people suspect that some of these trucks sat unsold for long periods of time on lots and thus could have fallen to the 40% threshold frequently, reducing the lifespan of the battery.

It is interesting that these Leaf's default to max charge if the battery monitoring system is disconnected and has me wondering if something similar could be done on the F-150 Lightnings to remedy the 12v battery issues?

 

[mcmancuso]

So I am wondering if the battery drain issue on my 2013 leaf is due to the cellular system and it never having signal because the device is too old to communicate with newer cellular towers. Would it harm anything to remove the cellular card in the vehicle?

You can just unplug the connector on the TCU and tape it over, there's no reason to have it plugged in at all any more. The car does not throw a CEL or anything when it's disconnected.

 

[NoahJ]

You can just unplug the connector on the TCU and tape it over, there's no reason to have it plugged in at all any more. The car does not throw a CEL or anything when it's disconnected.

Thank you for replying. I went and unplugged it after posting that. No errors and the battery stays charged for much longer. There is still something causing discharge though. Have not fully fixed the problem.