2014 (UK built) Leaf 12V battery charging strategy

Hi,
FYI: this is my first post on this forum. I would like to share some findings and find out some more info about how the 12V battery is charged.

I understand that the 12V battery is basically charged by the DC/DC converter from the traction battery. That can happen both while the traction battery is charged, but as wel during a normal drive cycle.

Last weekend I found by Leaf completely dead. Only a red symbol for the key system was flashing and the luggage compartiment could be opened. The car was connected through the AC charger inlet to a charge box.

I found out that the 12V battery only held around 6V. Deeply discharged. After recharging with a seperate battery loader I found it has 76% capacity left. It was not really bad, but getting worn, the guy from a a battery shop said. A normal car would start with it, but it might getting problems in future.

I put in another spare battery, which was somehow discharged but otherwise in good condition.
I tried to find out if the car would charge the 12V battery, but it did not at that time. only 13V on the poles in Ready mode, with selector in Park.

After that I did some measurements with that temporary battery.

After a day at work: connect via the nissan app and start a a preconditioning cycle. When arriving at the car, open bonnet and measure the battery. At that time 14.4V. Perfect charging voltage.
When coming home after half an hour of driving. Leave the gear selecter in Reverse. Handbrake on. Measure: at that time it was 13V.
Then I put on all 12V function I could imagione. Main headlight, fog light, rear fog light, seat heatings, max defrost on the windscreen, etc...
Still 13V. Appears to me that the DC charger must be fully operable, but it decides to not charge the 12V battery but only satisfy the demands of the 12V body system.

AFter that I put in the new battery I purchased. That one was somehow discharged when I bought it. Stand alone it delivered 12.4V at the poles. When I put it in it gave 12.3V (poles connected to the car system). Then I started a charge cycle. Now, it measured 14.4V at the poles.

So the car has at least some smart logic that decides when it will charge the 12V battery. Otherwise it will keep 13V at the poles which is not enough to charge, but it won't discharge either. So I regard that as a good neutral Voltage that will neither drain nor charge the 12V battery.

Still I am puzzeld why the 12V battery was not observed and charged while the traction battery was charging during the weekend and why it allowed the battery to drain completely. Since it was not really broken (as lead batteries can experience a sudden death with internal shortcut) I "would" had expected the car to initiate a charge cycle to keep the 12V battery charged

Does anyone have a description of this charging characteristic? Or is it just as "unsmart" as one might experience with other functions. That there is simply not a smart charging strategy or there is a bug that allows the 12V battery to drain. In that case I would like to understand which conditions might trigger the 12V battery not being charged.

I have read some topics about problems in earlier Leafs (2012) and that it should be pretty fine in newer (post 2013) Leafs, but I just want to be sure that the new battery holds a bit longer. Understand which habits I should evade.

BTW. I think 5 years of lifetime is still short for a lead acid battery. It has a production date from early 2014 so it must almost be the original battery.

The issue with the Leaf not always charging the 12 volt battery adequately extends through the 2013 model year. The biggest cause of a drained accessory battery is leaving the car plugged in but not charging, for example after charging has ended. This causes a phantom drain on the accessory battery (the car keeps checking the connection for activity) that the car isn't programmed to compensate for. If you don't do this, then I suggest you read through the numerous topics on this here. More to follow, from me and from others. Welcome.

LeftieBiker said:

The issue with the Leaf not always charging the 12 volt battery adequately extends through the 2013 model year. The biggest cause of a drained accessory battery is leaving the car plugged in but not charging, for example after charging has ended. This causes a phantom drain on the accessory battery (the car keeps checking the connection for activity) that the car isn't programmed to compensate for. If you don't do this, then I suggest you read through the numerous topics on this here. More to follow, from me and from others. Welcome.

Click to expand...

Hi LeftieBiker
I noticed in several forum threads that this issue was flagged for in 2012 MY Leafs. Not sure if it's still a problem on my model year.

I like to leave the it plugged for preconditioning without having to drain the traction battery. But if that triggers this, I may need to be more cautious. Since it appears that a preconditioning cycle even initiates a accessory battery charge cycle, it might be an ideal to schedule some preconditioning cycle just for the sake of charging the accessory battery, but that would drain the traction battery in case I forget to plug it in.

Just strange that this was the first time I encountered this problem. Maybe still a combination with wear on the accessory battery and this bug?

What would be the best way to get this kind of flaws reported to Nissan without having first to pay a Nissan reseller to have the problem debugged? My car is out of warranty. But IF Nissan would come with a software update, I would like to obtain if (and of course pay for that service).

Howdy mpostma, and welcome to the forum,

Your experience with the 12V has happened to me and others--it is a strange system that doesn't keep the aux battery fully charged. On an electric vehicle a weak, old or worn out aux battery can cause issues and throw trouble codes.

Sure the DC/DC converter will cause it to jump up to 14.4 at first while driving, but soon it will drop back down to 13V which is inadequate as you noted.

If you desire longer life then take countermeasures to fully charge the aux battery with a separate chargger periodically (weekly, bi-, monthly) as fits your budget. Keeping it fully charged and desulfated will extend the life.

p.s. Here is a good thread about the 12V battery. Unfortunately if you try to find this by doing a search, certain words are excluded and it will not show up.
https://www.mynissanleaf.com/viewtopic.php?t=22030

nlspace said:

p.s. Here is a good thread about the 12V battery. Unfortunately if you try to find this by doing a search, certain words are excluded and it will not show up.
https://www.mynissanleaf.com/viewtopic.php?t=22030

Click to expand...

Yep, sometimes it's easier to use Google search. e.g.:

"your search terms" site:www.mynissanleaf.com

Thanks for feedback. I have been searching around and ploughing in several threads. I have not found really clear info.

When the DC/DC converter will be started it will mostly supply the 12V system with 13V. IN some cases it will start with 14.4V and than after a while go back to 13V.

The need to charge is depending on how much 12V power is consumed when the DC converter is not active.
I read some thoughts about
- polling charging status when charging is finished.
- carwings communication taken car of by the Telematics unit.
- obviously using accesory mode.

Risky behaviour is to leaf the charger cable in a long time when the charge process is finished or to leave a OBD dongle connected to the OBD2 port. I suppose that polling car status with Nissan Connect can also be a risk.

Now I remember some things from the last weeks: not sure it had to do with this problem.
- I got a few times notification about a low battery on the remote control/key fob.
-I wondered if my charger box would go to green shine instead of green blink if I removed the charger cable from the box side. Ideed. But when connecting again it does not even initiate a short charge cycle. But maybe I triggered something that drained the battery.

As I wrote before: mornings are getting cold and I prefer to precondition the car before I drive a way. That causes me to leave the charge cable connected over the weeekend, just to be prepared for next drive (and then beging able to start a pre conditioning cycle with NissanCOnnect. That's apparently a habit I should change.

I actually do consider to not fully charge when I suppose not to use the car for a week or longer. But this is more about daily behaviour when the charge cable is connected for typically a day. It doesn't happen so often that we do not use the Leaf for more than a day. It's always the first to be pulled for whatever reason. But just this weekend I needed to drive som stuff to the junkyard with the bigger Volvo, skipping the Leaf.

I would like to do some more measurements and if needed do a bit more maintenance charging of the accessory battery. Just to hold the 12V battery in shape. Typically in this application where the DC/DC converter could really do smart charging, a lead battery should almost be able to live forever. Just keep it charged in a proper way.

The main problem might be to actually check the state of the accessory battery, which would probably mean switching of the dc/dc converter. That would be regarded as a safety risk, since if the 12V battery would be bad it might not be able to retain the voltage to keep the traction battery connected. Basically making the car completely dead if that would happen. So during READY State that would not be acceptable. This implies no accessory battery check possible during READY state. Maybe that would be solved if the DC converter voltage level could go down to 12V.

The battery monitor could check the accessory battery just before a drive cycle. Should the accessory battery be discharged (say less SOC than 90 %) it could just let the battery charge during the whole drive cycle. Not only 5 minutes. Which is never more than 2 hr anyway. Batteries are treated that way all the time in ICE cars. But maybe it's not about the risk to overcharge but energy reduction. Unnecessary charging the accessory battery might cost a few kms on the already hardly pressed range.

Every drive cycle the charge level could be checked again.
During charging it would be more easy. Just a matter of switching off the DC converter off after each hour, check how fast the accessory battery level goes down and then decide either to go to 13V float or continue charging.
When the DC converter is disabled (whether the charge cable is connected and finished charging, OR the charger cable is not disconnected) the battery management could choose to top up the accessory battery when if goes under i.e. 80% SOC. Of course it could come to a state where the traction battery should not be drained.
It could also choose to switch off carwings or any other accessories in the locking system in order to really prevent battery drainage.

All this text does however suggest that the charging algoritm requies a bit more attention then on a "simple" ICE. although mordern ICE cars are far from simple nowadays with smart alternators and whatever...

Still that 's no excuse: this is still one of the things that shows that "our" product is not really mature in every sense.

It would really flatter if Nissan would actively collect customer feedback and just solve these kind of bugs.

For my curiosity: what does the 12V system power?

I gues:
Body electronics like wipers, lighting, infotaiment, seat/steer heating, SRS is quite obvious.
How about the climate system? Heat pump compressors, cooling system, PTC?
What about chassis function: like the brake assistance systems, ESP, ABS? What about power steering?
Then of course the controls of the traction battery.

I mabye need to study a bit better. I am not a novice in car electronics (actually it's my profession) but I have not found so much clear documentation on the Leaf.

mpostma said:

For my curiosity: what does the 12V system power?

Click to expand...

The 12V system powers basically everything in the car except the heater, the air conditioning compressor, and the traction motor.

Lothsahn said:

mpostma said:

For my curiosity: what does the 12V system power?

Click to expand...

The 12V system powers basically everything in the car except the heater, the air conditioning compressor, and the traction motor.

Click to expand...

When the car is on and in Ready mode, the DC-DC converter uses power from the high voltage pack to power all of these. When the car is not in ready mode (including as you start it) the accessory battery powers everything. I know that Lothsahn knows this, I just wanted to make it clear for the original poster.

mpostma said:

When the DC/DC converter will be started it will mostly supply the 12V system with 13V. IN some cases it will start with 14.4V and than after a while go back to 13V.

Click to expand...

You'll also find that when the wipers are on, the 12V battery will be charging to about 13.8 to 14.4 volts.
My '13 Leaf has the original 12V battery, now six years old with 75K miles.

lorenfb said:

You'll also find that when the wipers are on, the 12V battery will be charging to about 13.8 to 14.4 volts.

Click to expand...

That was indeed an interesting observation.

Lothsahn said:

The 12V system powers basically everything in the car except the heater, the air conditioning compressor, and the traction motor.

Click to expand...

OK. if the 12V battery powers the steering and braking system, then it's rather obvious that the 12V supply system is really a safety critical system.

I'll need to rigg my car a little so I can observe the battery values during usage. Probably a ciragget ligher output connector with my multimeter. I suppose however that the cigarette lighter is relay switched, so I can in that way only visualise the battery voltage when the car is at least in accesorry mode.

Monitoring the battery voltage while driving won't work, because the DC-DC converter will keep the voltage in the normal range then, regardless of the state of the 12 volt battery - unless it fails completely and starts acting like a large resistor. The "rest" voltage is the best indicator of 12 volt battery state we have without having an auto parts shop test the battery. They will often do that for free.

mpostma: "BTW. I think 5 years of lifetime is still short for a lead acid battery. It has a production date from early 2014 so it must almost be the original battery"

I am aware that 12V battery longevity is largely dependent on ambient temps, but with the 12V battery QC issues I've read about here, and on other forums, I'd say 5 years is in fact longer than average for typical lead-acid battery life. I know you're simply curious about how the 12V battery is integrated into the charging system, but I'll just say that when my 2015 OEM battery failed (TX heat, at around 25k miles, IIRC) I just switched over to a Bosch AGM battery and stopped even thinking about it.

Also, in my experience, batteries "off the shelf" always need to be charged. You never know how long they've sat dormant

Interesting thread. I now know more than I thought I'd ever need to know about the Leaf charging system! I've always been an auto enthusiast, but at 65, slowly losing my interest...HAHA!!! (...and I've already forgotten most of what I just read...ARGH!!!)

mpostma said:

lorenfb said:

You'll also find that when the wipers are on, the 12V battery will be charging to about 13.8 to 14.4 volts.

Click to expand...

That was indeed an interesting observation.

Lothsahn said:

The 12V system powers basically everything in the car except the heater, the air conditioning compressor, and the traction motor.

Click to expand...

OK. if the 12V battery powers the steering and braking system, then it's rather obvious that the 12V supply system is really a safety critical system.

I'll need to rigg my car a little so I can observe the battery values during usage. Probably a ciragget ligher output connector with my multimeter. I suppose however that the cigarette lighter is relay switched, so I can in that way only visualise the battery voltage when the car is at least in accesorry mode.

Click to expand...

As Leftie noted, when the car is on in ready mode, the 12V power is supplied via the DC/DC converter. This *should* keep voltage levels nominal even if the battery is low, at least for operation.

That said, in certain cases, a weak or damaged battery acted as a power sink or possibly supplied insufficient voltage when the various modules were starting. These failures have resulted in failures of the braking system. Although rare, there are reports of Leaf's having weak or nearly non-existent brakes which went away when the 12V battery was replaced.

So yes, the 12V power is a safety critical system.

Some examples (keep in mind *some* of these may have been resolved with a brake controller firmware recall):
https://www.mynissanleaf.com/viewtopic.php?t=23746
https://mynissanleaf.com/viewtopic.php?f=30&t=16824&start=10
https://mynissanleaf.com/viewtopic.php?f=30&t=4467&start=40
https://www.mynissanleaf.com/viewtopic.php?t=18283&start=70
https://www.mynissanleaf.com/viewtopic.php?t=14859