In the ongoing saga of nursing my 12 volt battery, I have been testing various ways to maintain it without actually doing anything. I had suspected that my interactions with the car while "not driving" it was somehow affecting my 12 volt battery by altering when the LEAF boosts the battery when powered off. Things like grabbing something out of the car while its sitting in the garage was changing things so I decided it was time to test some scenarios to see if they made any difference. Now, my normal process was to plug in a few hours every day to keep my SOC in the 25-65% range during my 4 day work week. For my days off, it varies quite a bit. At this time of year the weather is too unpredictable to make plans more than a few days in advance. I am usually up early enough that any plans created for the day, I can simply plug in in the morning and have enough to do whatever it is I wanted to do. The larger battery means almost always having at least 75 miles of "emergency" range so adding more for longer excursions never takes more than a few hours.
Using LEAF Spy To Monitor 12 Volt Status.
On the LEAF Spy screen you can see the 12 volt battery status in the lower left corner of the 4th screen; the power meter or bar graphs showing GID, SOC, etc. I prefer the power meter to see the effects of seat heaters, A/C, etc. With LEAF Spy, you will see one of 3 basic modes
Tip; A lot of the displays shown in LEAF Spy can toggle to different data displays. Simply tap on the display to toggle thru the options.
12 Volt Battery Charging Automatically
This is the norm most people will see on nearly every start up. Voltage will be in the 14.4 volt range with a charge current running between 1-4 amps. In many cases, it drops to system voltage with minimal current within a few minutes.
This is the normal running state of the car. In this state, the 12 volt battery is essentially not being used. The DC system is providing the power and you will see the voltage around 13.04 volts with current usually well under 1 amp.
12 Volt Battery Charging Manually
This is the mode we will investigate the most. We can "force" charge the 12 volt by running the windshield wipers. I was using intermittent on the lowest setting. In this mode, the voltage is still in the 14.4 volt range but current varies from very low which means no charge being taken by the battery to several amps which means the battery is being boosted.
When Does The 12 Volt Charge?
The LEAF uses an algorithm along with a current feedback sensor connected to the negative battery terminal to charge the 12 volt battery. This can happen at any time. If it happens when the car is off and not charging, your charging light indicator on the driver's side will blink. Normally your charging light indicators tells you the approximate state of charge but starting from the passenger side. Now, I have seen this maybe 3-4 times in OVER a decade of LEAFing so trying to monitor this was something I attempted to do but abandoned. More work than it was worth.
Nissan's Insufficient 12 Volt Battery Management
As mentioned above, the 12 volt gets a boost on nearly every start up but sometimes the boost is very short including under a minute. If a charge is terminated just before start up, there is usually no boost at all. IOW; it starts up at 13.04 volts immediately. It was this observation that I based my tests on.
Test # 1; Charging Daily
This was easy. I normally do that any way. So I simply plugged in when I got up and on work days, the car charged between 70 and 90 minutes. On my days off, I charged between 45 mins and 3 hours.
The different charging times did not appear to make a difference.
44 of 52 days, I started immediately at system voltage. Which means 8 days I started at charge voltage
6 days, charge voltage lasted less than 1 minute. The other two days went just a bit longer.
I attempted a force charge all 52 days;
49 times, no charge occurred. The voltage rose to 14.4 volts but current was very small under .2 amps or less.
3 times, I was able to boost the battery for a few more minutes before current dropped below .5 amps.
In most cases, the 12 volt battery had the most charge the system would allow. For YEARS, I thought the initial 12 volt boost to 14.4 volts on startup happened automatically as some sort of battery check so the fact that most of the time, the car started at 13.04 volts was a bit of a surprise.
Test # 2; Not charging every day.
To do this, I had to throw out my SOC dogma and charge to 100% the day before my 4 day work week started. I did this twice charging Friday night to 100%, running SOC down to 75% on Saturday and starting my work week on Sunday. With a 28 mile RT commute, I have more than enough range to cover the entire week. During the test, I did not avoid detours but the most common detours I use don't add miles. In fact, one "detour" shortens my commute by .6 miles. I don't normally drive that way because it might be shorter but its a lot slower.
All 8 days saw automatic 12 volt boosting lasting anywhere from 3 minutes to 8 minutes.
On 7 days, I was also able to force charge as well lasting anywhere from 6 minutes to my ENTIRE 20 MINUTE DRIVE TO WORK.
Well, I think the issue is quite obvious. I expected to see more automatic boosting on start up, but what shocked me is the extensive forced charging AFTER the automatic charging ended. The worst happened 3 times; twice on Wednesday (end of the week) and once on Tues. Last week on the 14th of April, I pulled into work with my 12 volt still receiving 1.6 amps of charging current.
It would appear the algorithm is not designed to top off the battery. It appears to boost the battery on a timer. The current feedback sensor's likely role is to prevent overcharging.
What my tests didn't address is why am I able to park my car for 22 days (on my 40 kwh in July 2018) without issues? I have no easy way to test this because even at the far corner of my house, the car can still detect the fob and parking outside is not worth finding out more information.
Now we know we never have to take the fob out of our pocket when using the LEAF which means that the fob and the car are always communicating. Now most of this is short range communications that unlocks the door when you push the button, etc. So when you spend time away from the car, it eventually drops into a lower power mode disabling the short range sensors. My Prius would turn on the courtesy lights when I walked by it with my fob in my pocket so it was always sensing the fob so wondering how aware the LEAF was with the fob?
To test this, I locked the car at night which I normally never do since its always in the garage then in the morning, went out quickly and pushed the button to unlock the door and open it and found a few times that I had to attempt to open the door a 2nd time because it did not unlock in time. At first, I thought it was proof the car needed a split second to wake up. I also tried standing next to the door for a few seconds before pushing the unlock button and that also seemed to work a bit quicker.
In addition; I started monitoring how fast the door would unlock when I was out and about. Things like a 5 minute stop at the store, etc. It did appear the locking mechanism was somewhat quicker most of the time but without the ability to time it; hard to say.
Well, the title says it all really if you want the TLDR version. But charging every day is a challenge to some who have shorter range LEAFs. For me, its easy. I have a LEAF that provides about 8 times more range than I need most of the time. So having the "room" to charge even on days I am doing little or no driving, is easy because the car is never near a full charge unless I have an event planned. So now the question becomes "How bad off is my 12 volt battery really?"
Does my 12 volt really work that hard?
To find out, I decided to hit Electrify America right after the beginning of its free charge Earth Day promo which means 9 PM on the 21st since I am on the west coast, so jumped in my car, launched LEAF Spy and headed out for the HUGE journey of 3.2 miles to my "2nd closest" EA location (the other one is under construction so likely not working yet...)
I pulled up, turned off lights (something I normally do before I come to a full stop. Old habit from the 24 kwh days) popped the charge hatch, got out, plugged in and after less than a minute the charge started. So this is at the end of the day when the car hadn't sit for more than 2 hours after my drive home due to some shorter errands I had run after work. So this implies 12 volt battery should be in good shape as it would be getting boosted whenever Nissan felt it was needed so I'm good, right?
Things to note here;
You can see the significant drain on the 12 volt as soon as the car is shut off. Obviously this cannot be sustained very long and its simply what happens when the car is at a high state of readiness. I kinda covered it but you see the voltage dropping to 12.08 volts. How long will this go on, I don't know as LEAF Spy lost focus so I had to restart it which accounts for the 5 minute time gap.
I have been LEAFing over a decade on 5 different versions and have never had a 12 volt failure. So am I just being lucky or is there something I am doing unknowingly that has helped me avoid the issue?
After learning the above information, I realized my reducing time at high SOC meant that frequently the charging had finished within a few hours of my departure times. My extreme driving need from 2011 to 2018 meant charging every day was a must. Since 2018, I have been all about SOC management so I charge every day so I can keep from being too high (above 70% SOC) or too low (below 20%)
Since 12 volt failure has been a constant since 2011 on social media, I have visited this issue many times so I had a vague idea of what "should be ok for now" looked like and that seemed to be between 12.15 and 12.3 volts. But my Plus hasn't been doing as well as it hovers between 11.9 and 12.0 volts. That concerned me so a few times I removed the battery, put it on a charger and ran a full charge cycle on it but it never seemed to last more than a few days. This was way more effort than I or anyone else would want to invest especially if there was a way to lessen the risk so....
CHARGE EVERY DAY!