Degraded Battery Internatal Resistance and Regen Braking

I just had my battery replaced from a 4 bar loser. One of the issues I had with my leaf was the software update for the battery gauge seemed to tank my braking regen. But now, I don't think its the true culprit.

My old battery starting to have breaking regen issues around the time of the update, but it really was a few months after - basically when I lost my 3rd bar. At the end of its life, during a nice warm summer, I would start off at 100% charge with no regen available (normal), and start adding bubbles. I would only have two available for the first half of the range - meaning the first 6 fuel bars I would only have 2 bubbles of regen available. After the pack reach 50-60% remaining, I would get the third. The last bar never became available until below LBW (closer to VLBW). New battery is completely different. Regen starts off slow but by the time the pack reaches ~80% (two fuel bars down), I get all 4 bubbles and max regen.

This tells me the internal resistance that builds up in the battery is preventing regen braking, further reducing range. The program update may have changed how it responds to an more degraded battery, but it is definitely related to the internal resistance. Now here is the interesting part. Nissan, until recently never warrantied the pack against capacity, but only to performance. We all assumed this was directly related to power output, meaning a degraded battery couldn't loose any power acceleration bubbles (like when it gets to turtle), which it probably never would. BUT did we ever consider regen breaking as "performance"? After getting this new pack, I can tell a STARK difference in my ability to regen and cannot believe my older battery was preventing so much regen from happening (my carwing score for regen went from a 4 to a 1 with the older battery).

I just can't believe how much more regen I can get with a new battery

Actually, I'm not surprised at all... This was discussed in a thread here somewhere and was confirmed in a private sidebar discussion I had in Phoenix last year...

Pipcecil said:

I just can't believe how much more regen I can get with a new battery

Click to expand...

Pipcecil said:

I just can't believe how much more regen I can get with a new battery

Click to expand...

I noticed this too. Has your efficiency also increased ?

extremely. What makes it even nicer is no more brake jerking. Having the regen stop at 2 bubbles most of the time the physical breaks would engage quite early in the pedal push mapping. That usually resulted in some jerky/sticky breaking scenarios (yes I had the update to fix it). Now with full regen things go much much smoother. I can't believe a low capacity battery would affect the braking this much. Its night and day.

Discussed extensively here: What happened to my Regen?

Most people saw a drop in Hx value after the P3227 update - it seems that the LEAF uses the Hx value as a value to determine maximum regen combined with temperature and SOC.

drees said:

Most people saw a drop in Hx value after the P3227 update - it seems that the LEAF uses the Hx value as a value to determine maximum regen combined with temperature and SOC.

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+1

As I have suggested previously, I believe Hx after the P3227 update is likely now proportional to the admittance of the battery (as well as the capacity of the battery). Before the update, it was basically just proportional to remaining capacity.

I got the P3227 updated about six weeks ago. After all of the settling out of the values, capacity percentage has dropped only about 2% while Hx has dropped 12%. (Hx is now 74%.)

Likely the LEAF was allowing way to much regen on degraded batteries and thus was causing much more heating and therefore faster degradation than they were expected as the packs aged. The new change should help to slow the degradation rate on all batteries.

OTOH, I wonder if this change also causes the batteries to take longer to heat up in the cold in wintertime.

The battery's internal impedance has been mentioned as a proxy for capacity loss here;
Discuss data from the LEAF Battery app, and Comparisons - http://www.mynissanleaf.com/viewtopic.php?f=44&t=12789" onclick="window.open(this.href);return false;

RegGuheert said:

Likely the LEAF was allowing way to much regen on degraded batteries and thus was causing much more heating and therefore faster degradation than they were expected as the packs aged. The new change should help to slow the degradation rate on all batteries.

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Except that it doesn't appear that the '13s do this - they appear to allow more regen than the '11-12 LEAFs both before/after the P3227 update. Would love to see more data to confirm this, though.

IMO Nissan is being overly conservative with regen post P3227 update watching pack voltages under regen in regular (75-80F) temperatures - especially with the way that regen is significantly limited above 20-25 mph. At freeway speeds of 60 mph + and SOC over 80%, there is very little regen available if any.

drees said:

Except that it doesn't appear that the '13s do this - they appear to allow more regen than the '11-12 LEAFs both before/after the P3227 update. Would love to see more data to confirm this, though.

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Perhaps, but I wonder if that is true for a 2011 with a new pack. Perhaps Pipcecil has a way to do a comparison with a 2013 now that he has a new battery. Pipcecil?

Is it possibke that they put a different software in to go with your new battery? From what ive been reading, the batteries they have today are different that what they sold the car with. It stands to reason that when you change the battery type, you need to put a different software version in to do with it.

drees said:

IMO Nissan is being overly conservative with regen post P3227 update watching pack voltages under regen in regular (75-80F) temperatures - especially with the way that regen is significantly limited above 20-25 mph. At freeway speeds of 60 mph + and SOC over 80%, there is very little regen available if any.

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+1. I'm not sure why regen is often more limited than QC. Even in my case, living on a mountain, my sustained regen power level of ~15 kW is lower than QC power levels. Regen certainly makes the battery warmer, but not as much as QC'ing from LBW to, say, 60%.

Concerns about limited regen are another reason that I'd like a significantly larger battery pack in our next EV. 20 kW of regen is much less significant to an 85 kWh pack, even if it's somewhat degraded, than to a 24 kWh pack...

My pack had basically 100% capacity when I got the update, I could tell there was a big difference is regen under similar conditions.

It could be similar to the regen of a 2013 model, I am not for sure. All I know is: the battery pack (as told to me by the nissan hotline) is an older 2011/2012 pack, but was brand new. In addition, I knew the dealership had to install new software for the new battery pack - is there software that is stored IN the battery component itself? I thought all the software would be stored in the car. You can talk as many guesses as to what that software was.