Short introduction to the history of Isdera unique supercars, starting from Erator GTE of 60's up to Imperator, Spyder, modern Commendatore and incredible Autobahnkurier. Eberhard Schulz presented his first car in 1969. It was a Ford GT40 hand built replica called Erator GTE. The car made enough impression to grant Eberhard a job in Porsche. Next big step was the premiere of a concept car designed for Mercedes-Benz in 1978, model CW 311. Later it became a basis for own cars manufactured under the name Isdera. The new company was created in 1981 and next year presented barchetta type roadster, model Spyder 033. The prototype had Volkswagen Golf engine and Porsche 924 gearbox. With only 136hp power it was not very fast, therefore as the option Schulz foreseen Audi 2.1-litre 170hp turbo. Next models, Imperator 108i and Commendatore 112i, were true supercars with big V8 (Imperator) and V12 (Commendatore) Mercedes or AMG engines. First Imperator's engine had 5.0-litre capacity and delivered just 230hp, but that alone was enough to accelerate a light car to 60mph in less than 6 seconds. Later engines could have even more than 400hp. Commendatore in top specification was equipped with 6.9-litre AMG 600hp drive train combined with 6-speed manual transmission, allowing to reach 60mph below 3.5 sec. Finally in 2006 Schulz presented his own dream car, double engine, four wheel drive, huge Autobahnkurier 116i. The car truly out of this world. With summary of 10 liters displacement and 600hp net power packed in a retro style body, it remained just a prototype in the hands of its creator.
Recall that the data collection started a year after getting the car and 104 samples (about 2 samples per week) over a year, and only estimated to be evenly spaced two DCFC charging per week. But that’s close enough to real usage for this blog post (you didn't pay for it, did you?), and we extrapolate for many years using the same battery degradation equation from before. The years on x-axis are true years starting when the car was new. I extrapolated the data collected between year 1 to year 2 both ways, before data collection began (beginning of year 1 to year 0) and after last data collected (end of year 2 to end). One thing clear is that curves (green, blue, red) diverge significantly after about year 5. That means you won’t be able to tell which path the battery degradation is following until then. But even then, noisy data will make it hard to tell maybe until 5% divergence; raw data is fluctuating about 1kWh total, so 0.5 kWh deviations would be apparent.
Between blue and green, that occurs about year 8, the end of the warranty period. Linear decay (blue) assumes same number of charging per given time interval for all time, 104 DCFC per year plus X number of home charging. But if I’m to keep driving same number of miles per year, there will be more charging. Simply, each charge cycle would be capable of fewer miles due to degraded battery, and more charging is needed to drive the same number of miles. More charging per mile means more degraded battery. I plot this scenario as red plot. MrDRMorgan from SparkEV forum found that SparkEV battery warranty is to 65% in 8 years and 100K miles. If one follows linear trend (same number of charging per year, fewer miles driven each year), 65% would be reached well after eighth year. BUT if one drives the same number of miles by increasing the number of charging events, it could hit 65% in seventh year.
That could trigger the warranty service. It’s unknown what Chevy will do if that happens: they may not replace the battery with a new one, but one that is barely above 65% that will take it to eighth year. In any case, this is an unpleasant scenario to avoid. One might think that this is awful, but it may not be so bad. Biggest reason is that I have no idea what is the major contributor to capacity degradation. It may not be solely due to charge-discharge cycles that the red plot is based on. For most (all?) LiIon batteries, just letting it sit there would also cause degradation. If the major cause of degradation is time, then the degradation would follow blue curve (probably bit more since there'd be more charge-discharge cycles). How do you tell if the major contributor to degradation is time or charge-discharge cycles? If there are same model year cars with much different number of miles (more or less charge cycles) and in similar climate and "abuse" that show similar degradation, that would indicate more of time dependence.
Unfortunately, detailed battery capacity is hard to come by, not to mention finding other SparkEV with same usage pattern as mine. Even if the battery has degraded beyond 35% (65% remain), car would still be usable. How much is it usable depends on how far the DCFC stations are spaced. Currently in SoCal, DCFC between San Diego to Orange County is about 30 miles apart, which means car must be capable of 40 miles (10 miles as margin). From my first blog post, I estimated the car to last 10 years in amortizing purchase price / lease price. It seems it can barely reach 10 years with careful driving. All data and analysis are completely subjective, probably wrong, and should not be trusted! You might be wondering what prompted me to keep such meticulous data keeping after 1 year of use. I can assure you, it wasn’t because I wanted to put up with even more hassle of writing down charge data. I use eVgo almost exclusively for DCFC. Then about 1.5 year ago, I started receiving two emails that showed two different billing.
