Over the weekend Tesla CEO Elon Musk posted a bunch of tweets including the above charging advice. At least these tweets did not get him in trouble with the SEC, as he has done so many times over the last year. But this particular advice seems (to me) to not be the best advice. The advice against charging to 100% is based on something that is true for only a few miles, and if misread can lead folks to believe Musk gave us a blanket warning against charging to 100%.
The issue in the original tweet seemed to be a concern about the effect on battery life of charging to 100%. We’ve been told for years that, to extend the live of electric car battery packs, we should avoid charging to 100% and instead charge to 80% or 90%. But if we pay extra careful attention to the experts, they universally say the problem is not charging to 100%, but that the problem is keeping the car charged to 100% for a long time.
In other words, charging to 100% just before driving should be perfectly fine. Leaving the car for a couple weeks at a time on a charger that pegs the battery to 100%, like if you’re on a trip and left the car at home, that scenario is a problem for the lifetime of the battery pack.
The questioner says their commute is 160 miles — aside: that is 2 1/2 hours of driving time, which is simply an excessive commute, and that person should move closer to their job in order to have a healthier lifestyle — and the person is worried about having enough range to handle their commute plus miscellaneous other driving. The Standard Range Plus Model 3 has a range of 250 miles or so, and therefore they’ve got about 100 miles of cushion to handle other things.
Musk’s response talks about how regenerative braking won’t be very effective when the car is at 100% state of charge. While that’s true, the car won’t be at 100% state of charge for very long, and within a few miles the state of charge will fall enough for regenerative braking to be useful.
But — is worrying over a little bit of regenerative braking efficiency loss the best thing for Elon Musk to have discussed in that answer? I don’t think so. The person was obviously worried about a completely different subject from the answer given by Elon Musk.
Plus, this answer confused some journalists who attempted to write about it. They took Musk’s answer as a blanket warning against charging to 100% when his statement was about the efficiency of regenerative braking for a full battery pack.
What the original questioner should do is talk with their employer about installing a charging station at the office. Charging both at the office and at home increases the potential driving range considerably. They won’t have to worry about running low on power, and can set the car to charge to 90% and not worry about a thing.
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