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Is it ok to charge routinely to 100% capacity or would 80% be better for battery life ?
Hi,

I’ve been asking myself the same question. Looking at the various information available, it seems wise not to routinely charge to 100%, I use 80% as an approx target bearing in mind the battery capacity is actually about 5% more than is stated so they do leave a small margin already.
 

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I believe that it is recommended that you don't make a habit of charging to 100% and leaving the car at 100% for days on end. At the same time it is recommended to charge to 100% periodically. There are apparently two reasons why 100% is good every now and again, one is calibration of the State of Charge the other is battery or cell balancing.
  1. Battery calibration (it would be more accurate to call it Battery Management System (BMS) calibration) allows the BMS to keep better track of the 100% point and 0% point and from that make better estimates of when your journey is getting you close to 0%. If it can estimate better how far it is from 0% it can make a better guess as to the small remaining range.
  2. Battery balancing allows the BMS to ensure that cells in the battery-pack have all reached a similarly full level of charge.
Couple of links:
Andrew Till on Youtube describing the need for calibration
speakev.com battery balancing thread

I'm a new owner and I don't have the luxury of my own off-street parking. I also don't need to drive every day (far from it), but about monthly I need to drive a long distance. I've decided that I will only charge to 100% before a long journey. When I return I will probably only charge up to 80-90% and repeat that if I need to through the month. When I do charge to 100% I aim sometimes to leave the car on charge for extra time to allow the cell-balancing to do its job (you need to read the detail in the link or do research). I don't mind doing rapid DC charges to 80%, or if I am patient 90%, but I do my top-up to 100% on an AC charger. I'd use AC more if it was more convenient for where I live.
You generally only pay per kWh, so if the charging has become slow before 100% and some trickle at 100% it doesn't matter. In London that means avoiding the Source London charge-points which charge by the minute (and are expensive anyway).

As Kia say in the manual (and apparently Elon Musk is on record saying) AC charging is preferable for most of the time.
It is true that manufacturers have already left a small margin so 100% isn't really 100%, so there's already some safety margin. My attitude is that I don't need 100% most of the time so I don't go there often. I hope that by avoiding the battery sitting for days at 100% I can mitigate the fact that I need DC charging more often than users with home 7kW AC charging.

Optional reading:
There's an interesting article which uses graphs and tests of much smaller battery cells. In so many ways it doesn't hold true for a 2020+ era car with latest battery tech, clever BMS and safety margins on 0% and 100%.... but with that caveat it is a handy illustration of the effect of deep discharge and 100% charging.
Battery charging: Full versus Partial - 🔋PushEVs
 

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my 2017 soul EV is charged to 100% every day it's done 24,000 miles 12,000 of those by me since march, so I can assume it has stood unused more than it has been used and battery state of health is at 100%. From this I can only assume charging to 100% hasn't degraded the battery any.
 

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my 2017 soul EV is charged to 100% every day it's done 24,000 miles 12,000 of those by me since march, so I can assume it has stood unused more than it has been used and battery state of health is at 100%. From this I can only assume charging to 100% hasn't degraded the battery any.
Nice to know.
For me it would be a challenge to charge to 100% per day, so I'm content that I might be getting some benefit.
This guy is a battery chemistry expert and also says not to worry about charging to 100%, however he does point out that just operating the car between 80% and 100% is not good.
I suspect that there are many people who might be in that position if they have their own off-street parking, they might plug-in after nearly every journey and if those journeys are local they are (perhaps) doing their battery a disservice.
 
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