Cheap charging vs battery health

[Makro99]

Hi - I have the Octopus cheap overnight tariff.

Is there any risk to the battery of regularly charging only to 60% to maximise the cheap charging? We only use the car as a runaround in the week so rarely need 80% in a day, but wanted to know if battery health is affected?

[G43FAN]

Short answer I think is 'No', but how low is it getting on a daily basis?

What is your typical daily use?
How are you charging (7kW Home)? On a 7kW charger you should manage to charge 32kWh on Octopus 4 hour cheap window which gives about 50% battery after losses.

Best practice for this kind if battery tech would be keep between 20% and 80%. It is being kept at extremes of charge (high or low) that has most adverse effect.

Why 60% and not 80% though? I typically have charged most nights to top up to 80% for nearly 3 years now just for the peace of mind should I need to suddenly go somewhere further afield but on most days use less than 20% battery.

[Midgex]

In short, no.

It seems generally accepted and has sensible theory behind it that 50% is the point of least stress and distortion for a battery.
Extending that to 30-70% is generally thought, and seems reasonable to think, makes very little difference.
20-80% makes a working range declared ideal.

Previous generations of battery chemistries - particularly NiCd and still NiMHs - show an adverse memory effect, where a battery that is cycled between say 20 and 60% of nominal could become a battery of 60% of its nominal capacity until treated harshly. Li cells I gather do not do that, which is nice.


Also, rate:
Empirically, vehicles of one type where compared, between those frequently fast charged, and those not or rarely, for battery capacity deterioration. No significant difference. One of the American national institute places, I forget which one.

Mine spends time charging at 1.4kW because that maximises diversion from our solar panels vs drawing from the Grid, not because I'm averse to charging it at 7kW at home. And I felt actual excitement the first time I saw it getting 100kW on a trip. Sad, I know.

[Nerdy]

Actually yes best practice says keep it 20-80, with the argument keeping it between 40-60 would even be better (from a physical point of view)

[MotMot]

I’d argue that all the deg we’ve seen on id3’s so far is age related not to do with charging practices. I’ve not seen an example - even with high miles and loads of DC charging where it’s lost more than 10%.

Bear in mind the id3 is three years old now - and if there were a problem with degradation it would have started to surface now.

[Makro99]

Thanks all. Yes charging at home with 7.5GW. We usually only plug it in when it’s <30% as I was thinking 20-80 is the best.

[Scratch]

Actually yes best practice says keep it 20-80, with the argument keeping it between 40-60 would even be better (from a physical point of view)

I think VW quote 20-80% in the warmer months, but 40-80% in winter.

[StewartManley]

...charging at home with 7.5GW.

Careful. You could and up back in 1955...

[Mikeysid3]

I charge regularly at 40 -80%. But on long journeys I will keep as close as I can between 40 & 100%. The car is 2 1/2 years old and will do 220 in the summer & about 180/190 in the winter.

[RichyJ91]

Actually yes best practice says keep it 20-80, with the argument keeping it between 40-60 would even be better (from a physical point of view)

I think VW quote 20-80% in the warmer months, but 40-80% in winter.

Interesting. Got a link? Keen to know whether I should be charging back up when I hit 40% at the moment.

[Pablosammy]

Thanks all. Yes charging at home with 7.5GW. We usually only plug it in when it’s <30% as I was thinking 20-80 is the best.

I imagine charging at 7.5GW might damage the battery way more than going to 80% (as well as flattening the National grid when you plug it in)

[Scratch]

Actually yes best practice says keep it 20-80, with the argument keeping it between 40-60 would even be better (from a physical point of view)

I think VW quote 20-80% in the warmer months, but 40-80% in winter.

Interesting. Got a link? Keen to know whether I should be charging back up when I hit 40% at the moment.

Not a link exactly but a cut and paste from my online manual:

Examples for AC charging
Volkswagen recommends the following charging settings for AC charging:
Everyday driving - a long range is not required
Upper battery charge limit: maximum 80%.
Lower battery charge limit: a least 20% at mild to warm outside temperatures and 40% at cool to cold outside temperatures.
Driving long distances - a long range is required
Upper battery charge limit: 100 %.
Lower battery charge limit: a least 20% at mild to warm outside temperatures and 40% at cool to cold outside temperatures.
Avoid standing times and drive off immediately after charging.

[G43FAN]

Actually yes best practice says keep it 20-80, with the argument keeping it between 40-60 would even be better (from a physical point of view)

I think VW quote 20-80% in the warmer months, but 40-80% in winter.

Interesting. Got a link? Keen to know whether I should be charging back up when I hit 40% at the moment.

https://www.volkswagen.co.uk/en/electri ... ranty.html

[RichyJ91]

I think VW quote 20-80% in the warmer months, but 40-80% in winter.

Interesting. Got a link? Keen to know whether I should be charging back up when I hit 40% at the moment.

https://www.volkswagen.co.uk/en/electri ... ranty.html

Thanks for that, I’ve always known about the 80/20 but not the 80/40 rule. And I wasn’t that familiar with the concept of not sitting at 100% for long either. Cheers.

[RichyJ91]

I think VW quote 20-80% in the warmer months, but 40-80% in winter.

Interesting. Got a link? Keen to know whether I should be charging back up when I hit 40% at the moment.

Not a link exactly but a cut and paste from my online manual:

Examples for AC charging
Volkswagen recommends the following charging settings for AC charging:
Everyday driving - a long range is not required
Upper battery charge limit: maximum 80%.
Lower battery charge limit: a least 20% at mild to warm outside temperatures and 40% at cool to cold outside temperatures.
Driving long distances - a long range is required
Upper battery charge limit: 100 %.
Lower battery charge limit: a least 20% at mild to warm outside temperatures and 40% at cool to cold outside temperatures.
Avoid standing times and drive off immediately after charging.

Thanks Scratch, will adopt the new 80/40 guideline for this winter.

[EdinburghID3]

Interesting. Got a link? Keen to know whether I should be charging back up when I hit 40% at the moment.

https://www.volkswagen.co.uk/en/electri ... ranty.html

Thanks for that, I’ve always known about the 80/20 but not the 80/40 rule. And I wasn’t that familiar with the concept of not sitting at 100% for long either. Cheers.

I would imagine the 40% rule in winter is more to do with range and not leaving yourself stranded even on short commutes - Short journies is mainly how we use our car and the range is pretty low just now compared to summer so it makes sense to recommend 40% and allow a little buffer.