WetEV

1) Reserve for bad weather. Having to stop in bad weather for a charge wouldn't be ideal.

2) Batteries degrade with time and cycles, and keeping the car longer term. Still want to drive the route after years, and the battery is down to 80% of original capacity?

3) Deep cycling batteries reduce lifetime. This is why batteries have buffers. Note that "equivalent full cycles" is the same using the full range of the car, 204 miles (or whatever), and that could be one trip of 204 miles, 2 trips of 102 miles, or 10 trips of 20.4 miles.

Source is https://doi.org/10.1016/j.jpowsour.2013.09.143


1000 EFCs would be 204,000 miles. This shows the full range, buffers are not included but would remove the worst part of the cycles for lifetime.

Warnings: this is an older battery chemistry, that was in wide use a decade ago. I don't know about newer battery chemistries, as I'm no longer designing battery powered equipment. While this sort of characteristic was common between different chemistries then, it might be different in newer chemistries, and newer chemistries are different. I am not a real battery expert, I've once shared an office with one. This is cycling loss only, there is also time based (or calendar) loss to consider.

With this chart, notice that drastically more miles can be driven by using a smaller fraction of the battery's capacity. The ideal amount to use on daily trips is perhaps someplace between 20% and 50% between charges.

JNealCox

Run some ABRP scenarios. If you don't want to charge at all during that 140 mile trek, my concern would be with the return trip. You want to make sure you have enough in the tank to make it over the crest during that very inefficient climbing part of the trip.

skaven81

This isn't a fair look at the situation. That's a 1C charge curve -- that would mean deep cycling the battery at 95kW, or DC fast charging every time. L2 charging at home is ~0.1C and so the damage to the battery is GREATLY reduced. If anything, the chart you shared shows that even if you DCFC every day, that the battery will still retain a reasonable capacity after ~200k miles. To me, this actually supports my assertion and suggests that using the car in this way is just fine.

mtberman

Yep. A little off topic but degradation isn't really a relevant issue with the e-tron. Audi owners plug it in at home. Audi has been transparent about their conservative battery strategy. The e-tron could be incredibly fast and have a higher EPA range number, but they didn't go for any of that.

jim0607

I frequently drive from Bellevue to Cle Elum roundtrip (150 miles) in 35 degree wet roads. I'm heavy footed, have the heat pumping, music up, and in winter it can get close. I'll typically get home with about 10%-15% battery remaining. I will be doing the drive more frequently in snow, so I have purchased a set of snow tires and am curious how that will impact the range. I'm assuming I will have to be a little more cautious, but that said, the slower speeds might make up the difference for snow/snow tires. In the summer there is NO issue, I would get home with plenty of range. We also find that when we do fast charge, the car is typically full before we are ready to go!

WetEV

I agree, to a point. The paper's test conditions of 1C charge/discharge rate and 35C temperature are both higher than usual for the e-tron. Both charge rate and temperature will increase the rate at which the damage to the battery happens, so yes, reduction in capacity is slower than what that graph showed. And just as important, today's cells are better than the cells sold a decade ago. Charging at 0.1C is ideal, but boost power is 300kW or about a 3C discharge rate, and that's higher than ideal. Net impact? I don't know, ask a real battery expert.

My point wasn't any specific prediction as to life, but rather to point out that deep cycling batteries shorten life. That probably will not matter to anyone leasing, because they wouldn't be driving 340 miles a day very often. At 5 days a week, that's 85,000 miles a year. As the distance is getting close to what can be driven without an extra charge stop in bad weather, any loss of range will have an impact.