EV long evening journey - charge 100% overnight?
Discussion
Say you are going on a long journey in the evening but are not using car during the day, would you charge to 100% overnight at the cheap rate and let it sit all day?
Or 90% and top it up at normal rate before the journey?
Probably less of an issue in autumn temperatures but I felt a bit uncomfortable leaving the car at 100% all day in over 30c temps during the summer.
Am I over thinking it?
Or 90% and top it up at normal rate before the journey?
Probably less of an issue in autumn temperatures but I felt a bit uncomfortable leaving the car at 100% all day in over 30c temps during the summer.
Am I over thinking it?
I will be encountering this situation after 6 months for the first time in about 4 weeks and had the exact same scenario planned in my head, 90% and then an "expensive" 10% top up. Realistically it probably makes very minimal difference to the permanent degradation on the battery. The main damage is caused from leaving it at 100% for days on end. Up to 12 hours is highly likely to be fine, even more so if it's a one off. Or for the sake of £1 it could be worth the 90 and then 100 scenario if it makes you feel better. I'm still undecided which route I will take. Planning to take my R5 to 100k and beyond so trying maximise it's life where possible. 10k in after 6 months already and try to bounce between 20 and 80% where possible and if public charging AC charge at the destination to remove the need for rapid charging, plus typically cheaper.
Edited by Goatwidcoat on Wednesday 14th October 16:12
butchstewie said:
What do you think is going to happen?
Genuine question as I just got a Tesla so I'm likely to face this at some point and my assumption was that between the car and the charger it's just a complete non-issue.
Having the car sat at 100% for long periods - especially in high temperatures - is known to be bad for battery health, though whether 3/4 of a day counts I suppose is the question. I do this kind of journey once a month.Genuine question as I just got a Tesla so I'm likely to face this at some point and my assumption was that between the car and the charger it's just a complete non-issue.
Well I just AI'd it with your exact post and -
Claude said:
You're overthinking it a little, but your instinct is sound.
- Why your instinct is right:** Lithium-ion batteries age fastest when they sit at a high state of charge and a high temperature together. A battery parked at 100% in 30°C heat is about as unhappy as it gets while sitting still. That's why manufacturers suggest keeping daily charging around 80–90%.
- Why it barely matters here:** Ageing builds up over time. What counts is how many hours, across months and years, the battery spends full and hot. One day at 100% before a long trip is a tiny fraction of the battery's life and won't make a measurable difference. The real problem is leaving it at 100% every day as a habit. There's also a hidden buffer: the car's "100%" isn't the cells' true maximum, which softens things further.
- The cost side:** Adding the last 10% at peak rate on a typical 60–75 kWh battery is about 6–7 kWh. At a peak-versus-off-peak gap of 15–25p per kWh, that's roughly £1–2. The difference is small either way, so neither choice is a bad one.
- A middle option:** Many EVs and smart chargers let you set a departure time. You could charge to 90% overnight on the cheap rate, then schedule the last 10% to finish just before you leave. The battery spends almost no time full, and it's slightly warm when you set off, which helps efficiency and rapid charging on the trip. If the car can precondition the cabin while still plugged in, that helps too, especially in summer.
- One exception:** If your car has an LFP (lithium iron phosphate) battery, as some Tesla Model 3/Y, MG, and BYD models do, the advice flips. Manufacturers usually recommend charging LFP to 100% regularly, and these batteries tolerate sitting full much better. Your handbook or app will usually say which type you have.
- My take:** In autumn, charging to 100% on the cheap rate and leaving it all day is completely fine. In a heatwave, the 90%-plus-timed-top-up approach is a nice refinement if your car makes it easy, but doing it either way occasionally won't hurt the battery.
fooman said:
Having the car sat at 100% for long periods - especially in high temperatures - is known to be bad for battery health, though whether 3/4 of a day counts I suppose is the question. I do this kind of journey once a month.
Long periods means several weeks.I have only ever charged my car to 100% unless its on a rapid charger (due to the slowdown and cost more than anything) and I still get the same range as new.
I'm another one who thinks your overthinking this.
It's the equivalent of worrying that an occasional supermarket petrol fill up is worse than a branded petrol...
About every 6 weeks we do a longer journey and charge up to 100%, again often not leaving until after work.
Compared to the fast charging we use en-route, it's just a non issue.
It's the equivalent of worrying that an occasional supermarket petrol fill up is worse than a branded petrol...
About every 6 weeks we do a longer journey and charge up to 100%, again often not leaving until after work.
Compared to the fast charging we use en-route, it's just a non issue.
Depends on your tariff I guess, I'm with Scottish Power and I set how much charge I want and when I need it by and the apps works it out and any charging take place at my reduced rate. If you have a set window just charge to 100% and then let the car sit until you need it, you'll lose a few % maybe but that won't make a big difference to your journey.
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