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Range estimation fluctuation


Well-Known Member
Mar 14, 2013
(Mod Note: Not putting this in the "Decreasing rated range" thread because: 1) This is the opposite issue, and 2) that thread is long and meandering, altho similar issues have been discussed there).

There's been discussion here previously about the fluctuations in range estimates the car provides, and in particular the downward trend over time. We know that Li-ion cells lose some capacity over time/charge-cycles. But there are other factors at play in estimating cell capacity, and thus computing an estimated range.

This has been talked about in other threads. One of the claims I've made previously is that:

scaesare said:
There are 3 things in play when it comes to range:

1) Actual range loss due to battery degradation- This is to be expected as per Tesla. It's understood to be most significant early on in battery life and then taper more gradually over the remaining life of the cells.

2) Temporary range loss due to pack imbalance- This is a known issue with series style battery packs such as Tesla's. The loss is real in that the total pack range is diminished until the pack can be rebalanced. It's understood that the Model S can re-balance the pack, but when and under what circumstances is not completely known. Once the pack is in balance the range is restored.

3) Apparent range loss due to algorithm inaccuracy- This is simply visual inaccuracy due to the fact that "at rest" estimates of battery capacity are calculations, with a number of variables (temp, cell age, etc...). The greater the extremes of charge and discharge, and thus the larger sampling extent, the more accurate the algorithm may be. The converse is that shallower charge cycles result in less accuracy.

In addition there's been discussion about firmware upgrades "resetting" the algorithm and giving "false positives" in additional range estimation that subsequently disappears... as well as suspected algorithm changes that seem to affect things.

Because I'm of the belief that shallow charge cycles are best for the battery, I typically charge only to 60-70% during weekdays, and 90% on weekends. I'd rather a healthier battery than some imbalance or estimation error. My 70% charge yields 175-176 miles these days. I rarely drive below 30%.

I charged to 100% for probably only the 2nd time in a year or so yesterday. And this time I let it run for the final ~40 minutes to complete the charge, during what's assumed to be the balancing phase. My final range estimate at 100% was 253 miles when it completed, and actually 254 when I got in the car to leave an hour later (I've seen such "settling"before). I then drove it down to 14 miles left.

Today, my 70% charge rendered a 179 mile range estimate... 3-4 miles more than normal. It will be interesting to see how long that lasts.

So it's another data point that indicates that range "loss" that many people worry about is not actual battery loss, but factors 2 & 3 above. Thus I'm inclined to continue my current shallow-charge regimen.

I suspect if I were to repeat this cycle a number of times, the numbers might climb a bit more, including that for the 100% charge state.

I don't worry about it. I normally charge to 80% unless I need more range. However, the typical pattern is that I drive 25 miles to work, and 25-30 miles back, and have scheduled charging start at 02:30. So most of the day it sits much lower than 80%. I don't change this for the weekends unless I'm going to drive more, and if it sits all day at ~80% because I didn't drive it that day, it's not a big deal.
When my car was new, the only choices I had were (something like) Daily and Trip. When the slider was added, I started charging to 70% and ended my day at about 30% after my +/- 100 mile daily use for the reasons mentioned above. I noticed fairly significant loss of Rated Range when I did need to do a 100% charge for a trip. I can count the number of 100% charges I've done in over two years on one hand.

Recently, I did a 100% charge and let it complete, ran it down quite low and charged (Supercharged, actually) back to 90% on a recent road trip. I did about 8 Supercharges on my trip to 90% but actually saw my numbers reduce even further for some reason. I now see 215 Rated Miles at 90%.

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