Rolfe
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- Joined
- Apr 10, 2023
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- Location
- West Linton, Scotland
- Driving
- MG4 SE SR
Bjorn Nyland (Teslabjorn on YouTube) found that the MG4 with NMC battery would go for another 15 miles (might have been more) once the indicated state of charge reached 0%. That's usually enough to get you to a charge point.
We tried it on the hard shoulder it was beeping and warning us right down to 1% then 0% but it just kept on driving. We drove all the way to the next charge point and I suspect could have driven further
I watched that too. He was working in km, but I did the conversion and also came up with 15 miles.
My own car has an LFP battery, but when I drove it down to 4% one day I had no power restrictions, and all the way from 26% (which is where I started to take notice of what was going on) the % charge and the GOM dropped together at around 2 miles for every 1% battery charge, steadily, with no sudden alarming recalibration. I can't say it would do what the LR battery did with Bjorn, but so far as I took it, it was reassuring. At 15% charge the GOM was showing 28 miles, and I knew I was 23 miles from home. When I got home I was on 4% with 8 miles still on the GOM.
I've been discussing this in a thread in General Chat, and a couple of people posted videos taken by drivers who really did run out. What seemed to be consistent between the accounts was that one minute the GOM (and the % charge) looked as if they'd be OK, but then suddenly the car seemed to recalibrate and announce a very low SoC and very few (and diminishing) miles on the GOM.
One of the two cars involved I believe has an LFP battery, not sure about the other. What I have learned is that the LFP battery hates repeated partial charges without being allowed to balance at 100%. The charging profile of the battery is almost flat, making it very difficult for the BMS to figure out how much charge remains, and the balancing at 100% is important for the SoC and the GOM being reasonably accurate. If that isn't done, the instruments are more of less working blind, until very soon before the battery is empty the real state of affairs suddenly becomes obvious, and the recalibration comes as a severe shock to the driver.
I am suspicious that LFP (SR) owners are being influenced by all the "don't charge to 100% too often it's bad for the battery" talk that's aimed at NMC (LR) owners. They're not taking the battery to 100% and balancing every charge, hence their cars are giving an over-optimistic wild guess until the battery is more or less about to give out.
This is quite a long way off topic in this thread, just prompted by that last post. As you were!