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Thermal runaway
Posts: 18
Joined: Thu Apr 04, 2024 8:14 am

Post by Thermal runaway »

Dear all,

Are we in agreement that to constantly charge up to 100% and leaving it for long periods at this state of charge is bad for battery health?

If so, do we also agree that regularly running the battery down below 20% is similarly to be avoided?

Then, do we also agree the following?:

The (long) Journey Range of the Megane (indeed most EVs) should be considered to be charging up to 100% and running down to no less than 20%.

The Every Day Range should then be operating the car between 80% and 20%.

The industry are always quoting the Total Range which, is 100% to 0%.

They rarely mention the Emergency Range which, should be stated as 20% to 0%.

So, the EV-Database states the Megane as operating at around 3.9miles/kWh and I think this is probably about right.

This makes the various ranges of the Megane as follows:
Journey Range is up to 187 miles
Every Day Range is around 140 miles
Emergency range is 47 miles
Total Range is then about 234 miles

Winter temps might bring these down by 10% but probably not as much as 20%

Sound about right?

Best wishes!

natelittle
Posts: 38
Joined: Mon Jul 31, 2023 8:12 am

Post by natelittle »

Kind of, but not exactly. All EVs (including the Megane) have a battery capacity buffer that is entirely unusable. This is to maintain the health of the battery, so 100% useable is 60kWh, but the net capacity is somewhere around 65-66kWh - not sure on the exact, but I saw it in the spec sheet a long time ago.

The same goes for 0%. However the buffer is smaller here, but useable! You are right in saying that below 20% is bad for the battery though, but again, this is only a rule while leaving it at that %. Using it below 20% and then charging soon after is fine.

Generally though, because I want my battery to last for a long time, I too keep it between 20-80%, unless needed for long journeys. In which case it goes to 100% and I don't care where it falls to when I arrive, even if that means draining it to nearly empty.

Your calculations are pretty much spot on though for that efficiency. Although I normally see about 3.6/3.7 miles/kWh for my driving style (mostly motorways) so my range is a little less
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