Well, it happened to me this evening.
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I think I might have ruled out a few more explanations. First, there is no way this was a temperature issue. The day has been mild to warm, and the car was in the garage without any direct sunlight on it.
Second, it isn't a balancing issue. The car was fully charged up over Monday night/Tuesday morning and allowed plenty of time to balance. I checked that it had finished balancing before unplugging the charger.
Why would it be a 12v battery issue under the circumstances? Sure, the car hasn't been used since it was charged up, but that's little more than two days.
I only woke the car up to run it out of the garage to play with the light sensor cover. So it moved a few yards, that's all. I then got out and went round to the passenger side to fiddle with the cover. That's when I took the photo. I then got out and locked the car, before going inside to make a temporary dust cover for the sensor (hopefully I'll get a 3D printed replacement, or I can drill a hole in the original if not). I got back in the passenger side and fitted that. The whole operation didn't take long.
Once I was done I got back into the driver's seat to run the car back into the garage and out of the line of fire of the starlings raising a brood in the eaves. When the infotainment screen came on again, the readout was back to its normal green.
I'm interested in this post.
I've never heard of that before. Mine stays green the entire time - the lowest I've ever been is 19%, but it was still green then. I've never heard anyone else say that theirs changes green-amber-red in a regular manner. But it
makes sense for the thing to behave the way Stan1970 describes! Green when you have ample charge, amber when you drop below half-way, and red when you really should be thinking about where your next charge is coming from.
Could it be that it's meant to do that, that the ability of the indicator to turn orange is intended to come into play when you drop below half-full - but there is a stupid bug making it stay green almost always all the time, and just occasionally go amber for the sheer hell of it, irrespective of state of charge?