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I did a fairly lengthy (for me) journey home from England one day last week (325 miles) and the weather there was rather warm. I have a 40kWh 2018 Leaf. It was the first time I ever saw my battery temperature gauge go into the red but nothing changed about how the car was driving. There was no restriction in power output or speed. And there was no prominent warning light or message. If I had not been checking the temperature myself, I would never have known that it had gone into the red.

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I had done 252 miles by that point, having done four rapid charges en route, and was heading for home. I had been keeping an eye on the battery temperature during the charges and it never went into the red during charging. My last charge was on the Osprey at Alnwick. The charge was throttled back to 17kW, which I assumed was the car limiting the current to protect the battery. (The Osprey charger could give 50kW.)

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I have read a lot about ‘Rapidgate’ on this forum and elsewhere which had led me to believe that there was some kind of cliff edge, where the Leaf’s BMS would severely limit charging power on a third or subsequent rapid charge on the same day. However, in my experience, it just seems to regulate the power smoothly, gradually pulling back on charging power to keep the battery temperature out of the red. There was no ‘step change’ in charging power. And 17kW is not disastrous. It’s about 60mph (at 3.5 mile/kWh). For me, ‘Rapidgate’ does not seem to be too bad a problem while charging. If that is the slowest it gets, on a hot day down south, then I can live with that.

However, I had assumed that driving the car is much less onerous on the battery than rapid charging it. At 70mph I would only be drawing about 20kW, and the air flow under the car would help to cool the battery. So I was surprised to see the battery temperature continue to increase as I was driving. I was on the A1, which is limited to 60mph. With traffic, average speed is less than that.

When I saw that the battery temperature had gone into the red (top photo in this post), I wondered if the car would start to limit the traction current to protect the battery. But, no. I could not detect any constraint on power for accelerating and no speed limitation.

When I got home, I checked Leaf Spy and got these screenshots of the battery temperatures and condition. The timeline is incomplete because I did not have the dongle plugged in throughout the journey.

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The big increases were at 3.4 hours, when I used a FastNed rapid charger at Barnard Castle. And then at 5.5 hours, when I used the Osprey at Alnwick. (It was in the sun, hence the increase in outside temperature to 29C while stationary.)

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But my point is (a) my surprise that the peak temperature (54C) occurred not while on a rapid charger, but while I was driving. And (b) that the car had no protection in the BMS to limit current while driving to protect the battery, and no warning light or message to alert the driver to the high temperature.

So my questions are:
  • Does that match your experience with Rapidgate while charging and battery temperature while driving?
  • Should I have continued driving or should I have stopped to let the battery cool when I saw the gauge go into the red?
  • Is 54C harmful to a Li-ion battery?
I think power -is- limited in your first picture, only 13 grey segments are there on the power indicator, not all 14. Regen also looks like it’s limited to 5 of 7 blocks.
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