Gen Two LEAF BMS draft

 As soon as the Gen two LEAF batteries hit the streets with the 40 kwh 2018 model year, it was quickly apparent that Nissan had moved into an entirely new direction with battery management. Despite the pack being larger which implies more ability to take a faster charge longer, that did not happen. The DC charging knee on the 30 kwh packs was greater than 80% SOC. This made getting a significant boost in range in a reasonable amount of time quite easy.  One no longer had to wait until the SOC range was near zero to enjoy all the current the station had to provide. So it made sense that it would continue in 2018. But the knee dropped to no more than 70% SOC and depending on the temperature of the pack, could be as low as 45% SOC. As a reminder; the knee is the point on the charge curve when power stops rising because the current is dropping.  

Crazy BMS

The Gen One BMS would generate battery stats that bounced around on a near daily basis. changes of 2 or 3% within a few days was not uncommon. This led to some crazy theories of what was or wasn't good for battery health. But the  one thing that didn't seem to happen was a change in the range of the car. Maybe there was a change but I never noticed anything significant or more importantly anything "usable."  Now, I had 6 years experience with 24 kwh LEAFs and noticed a drop in range that was not all that extreme but in retrospect, the range was so limited that a bit more limitation didn't really impact my thinking. I had to charge on the road frequently to do my job when  the  pack was new so... nothing really changed when  I lost 10% of my range. 

On  the flipside, my 2016 S30 never had any discernible degradation over the nearly 30,000 miles I drove it and those miles were piled on VERY quickly. It was the best pack I had and I missed a great opportunity to find out how far Nissan had progressed. 

January 2018 116.2 miles on a single charge during "less than desirable" winter weather. Don't let that bar fool you. I was plugged into the EVgo DC at Tacoma Mall when I snapped this pix. 

82.34 ahr is the new pack parameter and that is where it was 400 miles and 3 days later 

when she was killed on the streets of Tacoma, WA. This was the 14 month LEAF Spy

shot. 

RapidGate, IceGate, And Adjustments

As we now know, DC charging was no longer predictable as it once was. The Gen two packs introduced a concept known as "RapidGate" which reduced the starting current on a DC charge when the temperature of the pack was "warm" at the beginning of the charge.  The 40 kwh  packs would see as little as 1/3rd the normal current on its 2nd or 3rd DC charge of the day.  Although the ramp down in current was more gradual, the slow rate of charge frequently doubled the time of the stop. 

But that was only half the story. I don't make it a habit of camping at charging stations. 95% of the time, I don't have the patience to sit in my car watching my SOC inch upwards so I have a routine where I do double duty on charging by taking care of personal needs and desires.  It was one of these times during the winter I noticed that I was already past the charging knee on my return 15 minutes later.  So I started tracking my starting battery temperature and when the knee happened and discovered "IceGate" where the charge starts to slow as low as 45% SOC instead of the near 70% we would see in ideal conditions when the pack was in the low to mid 80's ºF. 

Now the Bolt has issues in cold weather but speeds up when the pack heats up. The LEAF? Not so lucky. Several experiments both verified that RapidGate and IceGate are tied to the temperature of the pack when the charge begins.  So plug in, charge 5 minutes to gain a bit of warmth, unplug and restart the session? Well, tried that and it didn't work but only tried it twice. I am not done with that theory but that is a good 6 months down the road (I didn't do "any" DC charging this past winter) 

Gen Two BMS Goes In A Whole New Direction

 Gen One packs would retain their "new pack status" as much as several weeks so the parameters for ahr and GIDs were fairly well known parameters But the Gen 2 packs starting with the 40 kwh in 2018 changed all that.  As I always did, I recorded LEAF Spy stats the very first minute I sat in my new LEAF and I am glad I did because those numbers would not appear again.

The very next day after 93.5 miles of driving I was at 175.99 ahr and 99.77% SOH and the slow decline had begun.  So will your plus look like mine when you pick it up? Doubtful...in fact, VERY doubtful. Its been nearly 3½ years and there is still no real consensus on what the new Gen Two pack parameters are. Like my 40 kwh, the LEAF Plus BMS would run in two distinct modes;

Daily Mode

The ahr and SOH drops slowly or remains the same. They NEVER go up...EVER. Not even a single .01%. No amount of warm weather, temperature, DC charging, heavy use, or very light use would change this pattern.  All the things I just mentioned were used as theories on how to "boost your range" on the Gen One packs and yeah, they might have moved the battery stats up or down but an actual boost in range? Not sure anyone ever proved that. 

TBT, it was all quite boring. I mean I started only recording SOH and ahr only when it changed. My log was filled with a ton of blank spaces. Grasping straws, I started logging "longest stretch with no change" Yeah...I was that bored!

The Adjustment

Just as I was falling asleep at the log, some excitement came along... the bad kind. Just before my 3 month anniversary, I hopped in my car, started it and did the daily LEAF Spy recording and had to do a double take. 

I seriously thought I would drop a capacity bar before the end of the month! I had no idea what I was doing wrong! The only full charge the car ever had to this point was the one at the dealership when I picked it up (remember this!) 

When it finally stopped, I breathed a huge sigh of relief and continued on my merry way. It was winter which means a lot less driving than normal so I was over 70% SOC very infrequently as the plus range was more than enough to cover several days of usage even at that modest SOC.  But "exactly" 3 months later on April 25th, it did it again! This time it wasn't nearly as dramatic and only lasted 3 days but I was on pace to only have 55% capacity remaining at 100,000 miles. It was then I realized that something was off. VERY off. 

Experiments 

Since this was my 2nd Gen Two LEAF pack, I kinda already knew what to expect. Large early drop lasting 18-24 months that eventually drops to 1% a year more or less.  So when picking up my Plus, I started formulating experiments to see if charging/driving habits would change anything. By now, Nissan was very aware of LEAF Spy and its growing list of followers and I have to think they weren't extremely happy about that. As mentioned earlier, too many of us were using LEAF Spy stats to evaluate how well we were doing on our charging habits.

Gen one packs hid true pack parameters which explains why gen one packs would retain the new pack numbers for several weeks or more.