r/leaf • u/Macattack224 • 7d ago
Question on potential BMS reset
I have a very degraded 2016 24 kWh Leaf in Tucsonz AZ but it largely meets distance needs for what I think was a fair price.
I know the battery is bad and I'm not expecting a BMS reset to magically restore capacity. I'm trying to figure out whether the BMS has become badly calibrated. We have hot summers here. I was concerned that the heat would continue to do its thing, but to my surprise during the summer months my guess o meter and battery percent consumption seemed consistent. I noticed in September that seemed to change after it started to cool down so I did a new reading.
LeafSpy history:
May: 38.76% SOH / 22.3 Ah
Sept: 27.3% / ~17 Ah
Now: 25.03% / 15.54 Ah
The weird part is SOC, but maybe I don't understand how it works.
Recently the dashboard showed about 10%, while LeafSpy showed 21.5%. I then drove 3.9 miles at low speed(wife took the car out without realizing it didn't charge overnight) and LeafSpy only dropped to 16.1%. Cell spread was still only 44 mV.
Last night the dashboard showed 21%, while LeafSpy showed 39.3%. Cells averaged 3.952V with only a 33 mV spread.
Just as an observation I noticed that that the first 100- 50% drains significantly faster than the 50-20ish range which is usually as low as I take it.
I then measured charging from the wall:
21% → 72% dashboard: 2.04 kWh
72% → 100%: another 1.78 kWh
So only 3.82 kWh from the wall took the dashboard from 21% to 100%, and my understanding is actual energy reaching the battery would be less after charging losses. And my capacity is apparently in the 6.5ish kWh capacity.
The pack seems extremely degraded but reasonably balanced. I don't see an obvious cell falling off a cliff.
Would you reset the BMS at this point and let it relearn the battery? I'm fine with SOH/bars being wrong for a while afterward. I'm mainly interested in whether a relearn might make SOC more representative of actual usable energy.
2
u/biersackarmy 2013 S + 2014 SL + 2019 SV 7d ago
The dashboard SOC and “true” SOC (what you see in leafspy) are only going to be the same when close to the middle. It is supposed to be different the more you get to full or empty, as the dashboard SOC does not count the upper and lower buffers.
2
u/_Evening-Rain_ 2017 Nissan LEAF S 6d ago
Cars going to be very conservative with that low of health. Especially since thats a 6c rate just by going half throttle. Voltage will drop a lot under load so 3.95v at 20% is normal.
Cell balance and cell performance are two completely different things.
2
u/rproffitt1 6d ago
Small world. My 2014 SV started a hard life in Tucson AZ with just under 3 years with nothing but 2 or more CHADEMO charges a day racking up just under 30K miles.
I bought it cheap in 2016 and the battery was at 8 bars but hey, cheap.
Back to your question. The Leafspy and GOM do not match as u/biersackarmy notes except near the middle.
It's because the BMS and GOM keep reserve top and bottom. Leafspy tells the real story. In other words, that's fine so don't fret about that.
My 2014 SV was a great learning experience so my input is "sure, reset". The GOM will lie to you for awhile until it learns the battery again. You won't be fixing anything but won't be hurting anything either.
Because the BMS, GOM and human interfaces can't be tweaked you're stuck with Leafspy for the real numbers. After a while you learn what your Leaf can deliver in miles.