Leaf Service EV System Adventures with P0AA6-1A and a Suspect 12V Battery

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I never had sulphation problems on my Deep cycle pack, they were worked hard and charged hard, which I have found to be the best way to get the longest life out of a lead acid battery.
I did have one experience I cannot explain, however. I repaired the British buses that ran around Chicago back in the 80's. The owner would buy them in lots and have them shipped to the docks in Chicago.. On every shipment there was one bus that had something enough wrong with it, it became a parts bus.
One of these parts buses sat in the corner of the shop for a few year, being picked apart. They were 24 volt start/run and had 4 big six volts in the floor. The batteries were dead on arrival, and stayed that way for several years while the parts were removed, Finely I pulled the long dead batteries out and set them aside,. I decided to play around with them, I'd put one on the charger, 6 volt high, and as expected saw zero current. After a while, I turned it to 12 volt, and then 24 volt. I started to see current flowing and when it got to the 5 amp mark, I would turn it to the next lower setting. After about a day, the 6 volt was pulling about 10 amps from the charger, and after 24hrs it was up to about 30 amps.
Long and short of it, it took a week or more to bring the four six volts back to full charge and when place back into a bus, had no trouble starting it, in fact did much better than the two 8D batteries we normally installed. By all rights, the batteries should have been junk, and to this day I have no explanation as to why they weren't and went on to work for quiet some time.
I've worked on a lot of battery powered equipment, since and never saw another battery that could take the abuse the british ones did, and no ideas why they were able too. From then on the batteries got pulled out and charged, and were never assumed dead until charged and proved dead.
The first troubleshooting step for nearly every DTC listed in the EV Control System (EVC) section of the FSM:
• Turn power switch OFF and wait at least 20 seconds.
• Make sure that 12V battery voltage is 11 V or more.

That's why i always ask about the age and condition of the battery because an old, weak, or worn out, or depleted battery can cause a multitude of DTC faults across many systems in an EV, or an ICE car with a digital electronic control system.

DTC P0A94 for a DCDC converter fault can get triggered if the system voltage measures less than 12.48 V.

DTC P0AA6 for HV System Isolation fault has 22 steps in the troubleshooting guide.
The 12.48 voltage cut-off is for when the car is in the driving mode, The low cut-off in non driving mode is 10 volts for more than 10 sec.
So in laymans terms, battery can dip to 10 volts or even less on "starting" as long as within 10 sec the voltage rises above that. SO, the low voltage can be be expected to drop below the 10 volt limit for a brief time when starting in a worse case situation.
When "driving" (not in park) if the voltage drops to 12.48 volts it trips the code, which all makes sense, while driving the DC to DC is operating, if it can't keep up with load, for whatever reason, it trips the code.
It is the difference like an ICE car, expected voltage is lower when not operating but when driving it should be higher and if it is not you want the warning tripped sooner than when parked.
I've learned from reading this thread. Thank you to the contributors.

Specifically, I've learned that the 12V battery capacity (in usable ampere-hours, or A·h) may degrade much faster than the starting current it can provide (rated in CCA), with one being reduced to about 20% while the other's at about 90%. A LEAF, e-NV200 or practically any other EV doesn't need much CCA but it helps a lot for it to have a reasonable amount of A·h left. That's what makes the usual starter battery bench tests less useful than they are for the same batteries used for starting infernal combustion engines.

(The 20-hour rate for capacity dates from when lead-acid batteries were used for tasks such as the heaters of valve (tube) radios, as reserve power for telephone exchanges, and for submarines -- all of which needed a fairly long running time between battery charges. Now established as the standard, there are more disadvantages and costs for changing it than for keeping it.)
I'd caution against jumping to a simplistic conclusion that a load test is not effective. The take away should be the 12 volt system (connections, cables and charging method) have the same maintenance needs is in an ICE vehicle. That a poorly charged battery or a high resistance connection will cause problems.
The big difference is the symptoms will express differently because the current draw is less.
Most have seen or heard a car where either you turn on the key and everything looks fine, then when you turn to start either you hear a ratcheting noise or the car goes black, and may or may not come back on. While it can be a dead battery it also can indicate a poor connection.
EV's max draw on the battery is going to be less that an ICE cars battery, so the indications of a poor connection are not going to be as dramatic.
The Charging System looks at the current and voltage going into the battery and adjusts its output based on that info, but if the connection at the battery is poor, it will limit the current in and the voltage the battery gets from the charging system, and worse the charging system "sees" that the battery voltage is higher than it is and the current draw lower, so switches to float mode. The charging system can only "see" what the post connection sees, not what the actual battery post is at. SO clean the connections. It wouldn't be remiss to do it annually. A bad connection may pass a few amps, enough to start, but will also not allow the battery to get a full charge either. Only when it can't pass a few amps will you get a symptom. On an ICE car the starter draws a few 100 amps, and will show a poor connection earlier than a system that only draw a few amps.
In this case it was the fact that just about everything that could draw on the 12 volt was on (all heaters blowers and lights), before the problem showed itself. The fact the the battery passed a load test and could provide more than enough capacity to leave the parking lights on for 3 hrs before fading,suggests there is far more life to be had from the battery. The question to answer is what caused it to be so low that it couldn't handle the brief time between unplugging the EVSE and the start request? The obvious place to look is the battery connections. It most likely was a combo of a higher than acceptable voltage drop at the posts preventing a full recharge for quite some time, combined with a higher than normal load when no charging was provided.
Again, I think the problem is more likely 50/50 mix of a older battery and a connection problem. You can replace the battery, and depending on the battery terminals on the car you may solve both problems or just one. You can clean the terminals and solve 50% of the problem and that may be enough to get you several more years or not, just depends on the battery condition and how badly the poor charging that brought on the symptoms, sulphated the battery. You can do both and should be set for 7 years or more.
A LEAF, e-NV200 or practically any other EV doesn't need much CCA but it helps a lot for it to have a reasonable amount of A·h left.
So just put in a (smaller) Lithium starter battery (LiFePO4) and don't worry about all the other stuff. There are plenty of threads on the forum (you can search for my name and Lithium if you want), and the "it cost too much" complaint goes away as prices have come down...and the Lithium batteries last 2/3/4 times longer than the lead acid batteries (my Lithium 12v is over 10 years old).
Nothing wrong with that approach if that is what you want. For people like me, there are too many things that make it less than attractive.
cost is first.
I have 2 other vehicle that take the Gp51R battery so being able to change one out quickly if one fails in my other vehicles, makes sense.
A Li battery that would work in the Leaf wouldn't in the others.
I have two 6 volt vehicles and both were adapted to share the same battery group (just needed to widen the battery box) so there too I have a common battery type, for the same reasons. Even with low usage, I can start one in 0 degF weather and 15w-40 in the crankcase.
Give those facts, the Li battery doesn't hold the appeal to me that it does to you. Given my track record with the lifespan of FLA batteries, the pay back on a Li battery would be a long time in coming.
There is no "one size fits all" solution. Choices each have to make for themselves.
I am going to pay a visit to them today if possible to see how my loaner battery is doing. I've been very surprised in that to replace this SLA with just another Nissan OEM was going to cost +$210 plus whatever the dealership charges for labor. At first I thought it was just another "stealership" deal, but when I priced just to order a SLA replacement from some other battery shops and auto stores in the correct 51R form factor, I was shocked to see prices really are that high (+$210 range) now. 😲
If I go the AGM route for some better technology, the cost increases more. The core refund doesn't appear to be enough to lower the price that much, maybe $20 or more.

I must really be out the loop on lead battery prices because it seems not too long ago, batteries of this size could be had for $70 or less. 😥

It really does make using a Lithium replacement more financially feasible now. :unsure:

On a side note, I think for giggles, I am going to put their old battery into my wife's 2018 Leaf and see how it performs. :unsure:
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On a side note, I think for giggles, I am gong to put their old battery into my wife's 2018 Leaf and see how it performs. :unsure:
Aw you thought of her for Valentines day, aren't you sweet!😘
I'd still suggest putting a meter on the charging system before calling it good.
I haven't bought a new battery in several years, so haven't kept pace with where the prices are at. Last one I purchased was several years ago to go in my Saab turbo, I needed the slim form factor to get as much distance from the turbo as possible. Stock had a complicated heat shield set -up to shield the battery from the turbo heat. As My car had the turbo engine transplanted in (Before I owned it) it was missing the heat shield. I made one from sheet metal, but without an insulation layer sandwiched inside, it would have still cooked any battery placed against the inside of the shield. An air gap and air scoop from behind the grill keep the turbo heat away from the gp 51, and the car starts fine with it.
Just tried to look up my old supplier, turns out they were bought out by Continental and are not the same place I used to deal with.
Looking on line prices range from $80 and change to $720 (720 is a Li the cheap is LA) but most seam in the low $100's still for a flooded cell.
I had a good experience with my old supplier, and trusted the product they sold. Not sure where I'd go for a battery now, the new owners may be ok, or not.
For me the 1st criteria for LA is it must be FLA and not SLA.
I was looking on "Antigravity" battery site, their Gp 51 is only 24 amp/hr or 30 amp/hr depending on which you choose. but what really got me was:
No Acid or Heavy Metals such as Lead, Cadmium, or Mercury.
Ah, but Lithium is a heavy metal! No it isn't the three named, but it is a heavy metal.
Looks like I may be wrong about it being "a heavy metal" but it is a toxic metal like heavy metals are. Trace amounts are ok and beneficial is but can be just as dangerous as the heavies.
I was thinking along the lines of "heavy water" and Lithium's use in nuclear reactions. Been a brave number of years since I last sat in a chemistry class!
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My wife is the proud (and unknowing) owner of this Nissan OEM 4 year old, questionable 12V SLA battery. I installed it a few days ago and told her to drive it around like normal and I'll check on it every now and then. I can finally test that +9 year old 12V LiFePO4 battery to see how it does for a capacity test. Luckily, test for Lithium are a lot faster, I'll know the results in less than an hour. :devilish:
I'm lucky in that her Leaf often sits idle for a few days over the weekend, she does most of her driving during the week-days for work. 🫥
Well, some bad results to report, not on the 12V Lithium as I have not had the chance to test it, but on the original 12V SLA at the heart of this discussion. This "suspect' 12V SLA was installed into my wife's 2018 Leaf Thursday night. She drove around on it Friday and since Friday night it has been sitting in our driveway. So I figured, nearly 48 hours of nothing might be good time to test it and see how it performs. I was gong to replicate what my relative was doing when it failed for them. So first I got a voltage reading with it doing nothing. I accessed the hood to do this as I don't want cabin lights on, computer waiting for keys, etc. I waited for about 30 minutes before tinkering under the hood to give it time to "deep sleep" at the lowest power level.

My initial readings were not promising. Only 12.04V and it's warm outside and has been for a few days now. But...no load, so no problem.

Next, I get in, put the her Leaf into standby (two power button presses) to begin simulating what my relative had running at the time. All accessories were off, so I pressed the "auto" button on the climate control and the cabin fan came on. Got some voltage readings from both the meter and LeafSpy. Not looking great, but still above 11.0V at least. :cautious:


I then turn on everything they had on, lights, radio, seat heater, and steering wheel heater. I then get some quick voltage readings from my meter and LeafSpy.


Yeah, the voltage was starting to fall, I got it captured around 11.64V, but it was like watching a clock count down seconds. I figured I would just wait to see what happens, maybe it will stabilize a little? I did not have to wait long, it took no more than 15 seconds before the voltage dropped so rapidly that her Leaf actually died. :eek:

What followed was exactly what my relative told me, the dash went out, cabin light went out, then cabin light came back and I could hear all the accessory relays clicking, the dash was beeping at me and had the screen reset to the "push in the brakes and press start" message on the dash, etc. I didn't get to see what my meter showed for voltage because it happened too fast, but LeafSpy certainly showed a drop below 10.5V before it lost connection and had to re-connect.

Soooo... to avoid stranding my wife and facing her wrath 😵‍💫, I ran inside to go get the 12V battery charger and clamp it on. It just needs to work for one more day, lol. I don't know what capacity this SLA was at because as luck would have it, she needs to use it later to visit a friend, so I won't be able to preform another capacity test right now because I am really, really interested to see how much it had left.

To add to this, I know why it died at 10.5V because that is the voltage the Leaf will try to engage the traction battery to begin charging the 12V battery back up. So it turns out it did not have enough power left to do this and died. No codes were generated so at least that is a positive side of this experience. :censored:
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Seams like you have an answer. The interesting part is: it didn't start charging and carrying the load from the 12 volt when the car was in stand-by (on but not ready) which from what I have read in the manual, it should have as long as it is park.
The other take away is you can skate for a long time on a questionable battery as long as you don't run the the pre-heat on it.
Sometime I'll play a little with mine, and see when it start charging the 12 volt.
AFAIK there isn't a "drops to 10.5 volts" then it starts charging, set point. I haven't seen that anywhere in the manual when researching the 12 volt charge protocol. Everything (and I posted a screen shot of that page somewhere) in the manual say, as long as it is in park, it will charge the 12 volt with the key on, not ready, with the key off charging off a EVSE or DC fast charge, and with the key on ready. It only keeps charging in any gear other than park with the key on ready position.
So either the manual is wrong, or something else is going on. I tested my Leaf, and as far as I went, it preformed like the manual said it would. It would charge off the EVSE and when the key was on, car in park.
Even when parked, key off, it charges for 4 min every 24hrs that it doesn't see any load (no door opening etc).
Even with it getting quite cold here, I very rarely try the pre-heat function. It just doesn't seam worth the hassle.
I am going to have to break out the meter and see what happens when.
I know you can set the priority for the EVSE, to either run the charger or the pre-heater, and I don't know if or how that plays into it.
AFAIK there isn't a "drops to 10.5 volts" then it starts charging, set point. I haven't seen that anywhere in the manual when researching the 12 volt charge protocol.
The only reason I know is that I tested it years back by draining the 12V battery and monitoring the voltage to see when it engages the big battery for DC-DC power. On my 2013 Leaf it was 10.5 V exactly, similar on my 2020 Leaf, I'm pretty sure it would be the same on my wife's 2018, but to be fair, I have not done a direct test :unsure: , so it's possible it's different, but seems illogical to change that for one model year.

The easier way to do this is put the Leaf in standby (two power presses), starting monitoring the 12V voltage and then put a bunch of waste loads on the battery to try to "drag" it down to 10.5V and you'll hear the contactors engage and then all of sudden you have a high voltage on the 12V battery from it trying to blast in a lot of power for charging. It also activates the middle Blue light on the dash when it happens, so you'll know you hit it just right. :LOL:

If I can feather it just right with this "suspect" battery, I can probably provide an example video to demonstrate. Good way to test if the 2018 Leaf works like the others. Provided the weather holds out, it is suppose to be freezing again for the rest of the week according to the forecast. 😑
I'll have to go out and try and replicate it. When I was playing around the last time, it would go to 14.5 volts and then taper down to 13.3 and hold steady, I could bump it back by turning on the wipers. Plug in the EVSE same thing.
May be a few days before I get around to running test.
I was able to get a video before all the freezing weather arrived. Basically, made sure I started with a fully charged 12V because I was worried this would die before it could show the process. So I was running the cabin fan and the rear window defroster to create as much load as I could without tanking the battery too fast. It needed to have enough power left over to switch on the HV battery or else the demonstration would fail. :LOL:

So I can at least confirm that the 2013, 2018, and 2020 Leaf still work this way in regards to monitoring the 12V battery for low voltage when the HV battery is not energized.

I was also incorrect, it's not the middle blue light on the dash, but the blue light closest to the driver.

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I'm not able to reproduce the result I got, or thought I got the other day.
Today I sat waiting for my wife while she was at appt. I was listening to a CD for over an hour. The car would turn off about every 15 min, if I didn't do something to let it know I was still there. (Hit the brakes or???)
When I got home I got out the meter. Would charge at 14.5 and not taper like last time, likely because the battery was not fully charged from sitting with the CD player on.
I could not get it to 12 volt charge from the EVSE when plugged in but on the timer (for 12:00 AM start)
I couldn't get it to 12 volt charge when the key was on, but not ready, red battery warning light on the dash was illuminated. Only would charge key-on ready.
I found this odd, and contrary to what the manual said should happen. As long as the car is in park, and not neutral, it should charge. That is what I thought i saw a few days ago when I checked.
So either I am mis reading the manual or ?