What follows is my mostly opinion.Silverfish wrote:@WetEV, how can you tell the difference between fooling the BMS and doing things that are actually good for your battery? I've read that the LeafSpy battery stats are kind of meaningless over the short term, like a few months, but I'd think that over 15 months, they would at least mean something.WetEV wrote:Leafspy just reports on what the BMS estimates the battery capacity is. The BMS can be fooled. Fooling the BMS doesn't improve the battery. Resetting the BMS doesn't improve capacity. Recharge and range tests confirm this.
DCQC and high discharge and regeneration probably wear the battery faster.
In the 2+ months I've had my car, I have noticed that babying the battery makes the LeafSpy stats go down, and getting the car to really stretch its legs -- longer distances, freeway driving, deeper discharges and recharges -- makes them go up a bit. I get that those numbers may not be accurate, but in that case, how can I measure and determine what's good for my car?
I think that the battery true capacity is mostly declining with time. Faster for deep discharge/charge cycles, faster for high rates of charge/discharge, faster at high levels of charge or low levels of charge and faster at higher temperatures. Slightly faster for the first 5% of decline, then slower, then faster somewhere below 70% capacity.
I think that most variation of the BMS statistics that LeafSpy reports is just inaccuracies in the estimate, and not real changes. I don't have measurements accurate enough to prove this. In a few months last fall, I measured my LEAF's battery capacity with a L2 recharge test at temperature of 20C, then tried to increase the BMS estimate by DCQC, faster driving, deeper discharge and a few other tricks, then to tried to reduce the BMS estimate by slow L2 charge (8 Amp L2), local driving only, keeping charge near 50%, shallow charge cycles. The result was that the BMS estimate can be 12% or more larger capacity than real, and perhaps 2% to 3% percent less than real. This is making the assumption that the real capacity doesn't change much over a few months, and variations in driving/charging don't actually change real capacity.
So how could I take measurements with the BMS that vary +12% to -3% from real capacity and find the trend of declining capacity which is about 2.5% to 3% a year in my case? With at least a few months every year of consistent driving in consistent temperatures and such and a few years of records, I think this is a realistic goal, however isn't easy as your life changes, and as year to year weather may be different. This gets harder on a shorter term basis, but on a year to year period might be fairly accurate.
So how could find the smaller variations in that small trend caused by different charging rates, driving styles, depth of charge/discharge cycles and so on? What makes this problem even worse is that the BMS software has been updated at least on some cars, the battery chemistry has changed over the years and so forth... I don't think there is an easy way to use BMS statistics to really tell what's good for the car. It seems to me that it would take years and multiple cars to get to a believable answer. It would be easier to use a more accurate way of measuring battery capacity, and multiple cars driven in the same conditions with different charge rates, depth of charge/discharge cycles, etc. But with one car? You are looking at a tiny needle in a large haystack. The haystack is fuzzed up because of BMS inaccuracy. I don't think you can tell the difference between "fooling the BMS and doing things that are actually good for your battery", at least with one car and a reasonable amount of time.