fewer/higher VS frequent/mini charging sessions?

[smoothound]

Sorry if this fish has been fried before.....

During periods when daily usage is low but frequent - For battery longevity - and assuming 7kw single-phase charging ....

Is it better to top-up charge a little every day - keeping say between 40-60%ish? - Or - Leave it a few days and do a less frequent up to 85%ish type charge when charge drops to around 15%ish?

So, daily mini 'cycles' - vs - fewer larger 'cycles' (not dropping below 15%ish or exceeding 85%ish)

or would it not make much difference?

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[Pozuelo]

I think it makes little difference. I would charge to 85% when it drops to 20-25%. Not any lower, also you might need the range unexpectedly.

 

[bsclywilly]

Lots of good information at this site on different factors affecting battery life.

https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries

The quick answer to your question is more frequent charge cycles at 40–60% SOC is going to be better for battery health. Both depth of discharge and higher state of charge have negative effects on battery life. And the number of charge cycles can increase exponentially when keeping the DOD and SOC in a middle level.

Fig.6 in the above link sums it up best. If you draw a horizontal line across ~90% capacity, the 75-65% case can cycle 8500 times and the 85-25% case can only cycle about 2000 times before reaching the same capacity drop. Just to pick one comparison example.

Definitely read the details starting from Fig2 in the link.

 

[Pozuelo]

Not the best example in my opinion. If you charge 8500 times and raise by 10% the SOC it implies you have added about 8.4kw x 8500 times which equates to 71,4Mw. However if you raise state of charge by 60% it means you have increased 50,2kw x 2000 times which is 100,4Mw. So same battery capacity drop while adding 30% less useable energy.

 

[smoothound]

Thanks folks - Much appreciated.

Some useful data there - I will run up a spreadsheet when I get chance and have a looksee.

 

[bsclywilly]

Not the best example in my opinion. If you charge 8500 times and raise by 10% the SOC it implies you have added about 8.4kw x 8500 times which equates to 71,4Mw. However if you raise state of charge by 60% it means you have increased 50,2kw x 2000 times which is 100,4Mw. So same battery capacity drop while adding 30% less useable energy.

Oh, yeah you’re right. That was not the best example because it’s still at a high state of capacity. But because the slope of those curves are diverging, as you get to lower battery capacity, the advantages become more clear.

If you did your same calculation for the 75-45 curve and the 85-25 and normalized it for the same Wh then the difference is more clear. The75-45 would be a few percent healthier than the 85-25 curve.

 

[McgR]

Not the best example in my opinion. If you charge 8500 times and raise by 10% the SOC it implies you have added about 8.4kw x 8500 times which equates to 71,4Mw. However if you raise state of charge by 60% it means you have increased 50,2kw x 2000 times which is 100,4Mw. So same battery capacity drop while adding 30% less useable energy.

I was thinking exactly the same 8.500 x 10% is less charge than 2000 x 60%. In this example it would be better to let it drop to a level that is comfortable for your need (but more than 10-15%) and charge to 85% when this level is reached.

I have a 22 kw home charger but I have set it to 8 kw. This is more than fast enough to charge it over night once a week. I think slow charging might be better.

And to optimize battery life
Avoid fast chargers
Avoid charging with high ambient temperatures
Avoid keeping the battery at 100% without using it and don’t stay to low either.

 

[W1NGE]

Sorry if this fish has been fried before.....

During periods when daily usage is low but frequent - For battery longevity - and assuming 7kw single-phase charging ....

Is it better to top-up charge a little every day - keeping say between 40-60%ish? - Or - Leave it a few days and do a less frequent up to 85%ish type charge when charge drops to around 15%ish?

So, daily mini 'cycles' - vs - fewer larger 'cycles' (not dropping below 15%ish or exceeding 85%ish)

or would it not make much difference?

Don't sweat it and besides you won't keep the car beyond the battery warranty of 8 years!

Full cycle charging leads to a degree of impairment but daily charging to 85% will be just fine.

 

[smoothound]

Don't sweat it and besides you won't keep the car beyond the battery warranty of 8 years!

Full cycle charging leads to a degree of impairment but daily charging to 85% will be just fine.

Not sweating it - thanks - just interested - and try to make informed decisions where possible.

 

[McgR]

Lots of good information at this site on different factors affecting battery life.

https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries

The quick answer to your question is more frequent charge cycles at 40–60% SOC is going to be better for battery health. Both depth of discharge and higher state of charge have negative effects on battery life. And the number of charge cycles can increase exponentially when keeping the DOD and SOC in a middle level.

Fig.6 in the above link sums it up best. If you draw a horizontal line across ~90% capacity, the 75-65% case can cycle 8500 times and the 85-25% case can only cycle about 2000 times before reaching the same capacity drop. Just to pick one comparison example.

Definitely read the details starting from Fig2 in the link.

I think the most useful is to compare % of charge and battery level.

60% charging from 25-85 is better for battery SoH than 40-100 and same 50% charging from 25-75 is better than 50-100.

worst is 50-100 it has the same SoH after 4000 charges as 40-100 but with 10% less charge.

so avoid 100% and from this graph it would be best to keep it between 25 and 75%. I think I might just do that. I don’t need 85% in my daily use and with my 22 kw home charger I can charge quickly if necessary

 

[smoothound]

I think the most useful is to compare % of charge and battery level.

60% charging from 25-85 is better for battery SoH than 40-100 and same 50% charging from 25-75 is better than 50-100.

worst is 50-100 it has the same SoH after 4000 charges as 40-100 but with 10% less charge.

so avoid 100% and from this graph it would be best to keep it between 25 and 75%. I think I might just do that. I don’t need 85% in my daily use and with my 22 kw home charger I can charge quickly if necessary

Tha McgR - that was my situation and way of thinking too - for the majority of days I will only use mebbies ~10-15% - So will keep it mid-range - and more frequent shorter charging. Cheers

 

[McgR]

Tha McgR - that was my situation and way of thinking too - for the majority of days I will only use mebbies ~10-15% - So will keep it mid-range - and more frequent shorter charging. Cheers

I currently charge to 85% when I am below 50. Which is once every 3-5 days.
I am the same as you. Want to know what is best. But I also know chances are around 0% that I will be driving it long enough to notice a difference and it is a lease. But that doesn’t mean I can’t take care of the battery for the next owner if it doesn’t cost me any effort.

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