Optimal Battery Charging for best longevity

[2101Guy]

Yes I realize that Elon tweeted 90% charging regularly, is fine. Im also aware of Tesla's "a happy Tesla is a plugged in tesla", motto. Also aware they recommend plugging in every night.

But I've always thought that Lithium batteries typically have limited charge/discharge cycles before degradation starts to occur.

Lets assume I drive 100 miles total per week. Lets also assume I charge to 100% once per quarter for a quarterly road trip, but i charge at the lower limits below, regularly.

All other factors being equal, which scenario below is best for the battery/ensures best longevity for the battery:

- Plug in every night and charge to 90%
- Plug in once per week to 80%?

 

[P85_DA]

In six years of Tesla ownership S and X ..I have found the best strategy is just drive and enjoy the vehicle ...I have charged daily mainly to 80 or 90% ..I found that even babying the battery you still cant control any software updates that Tesla will do in future ..there is a long thread on this in the forum where Tesla throttled down battery with software

 

[SSonnentag]

Optimal: 50% charge, never driven, left plugged in. Any variance from that decreases longevity, roughly logarithmically based upon how much the charge deviates from 50%..

Heat is a factor too. Fast charging increases heat. Racing increases heat. The desert sun increases heat.

 

[2101Guy]

Optimal: 50% charge, never driven, left plugged in. Any variance from that decreases longevity, roughly logarithmically based upon how much the charge deviates from 50%..

Heat is a factor too. Fast charging increases heat. Racing increases heat. The desert sun increases heat.

totally understood. But purely from a battery science aspect, still curious as to whether charge/discharge cycles are any factor at all in longevity

 

[Lasttoy]

When I bought my antique, Tesla said low 25 miles,high 175 miles. It would last longer. So far 8yrs, over 2000 charges, I'm still good.
My warranty runs out soon. So now I pray.

 

[ucmndd]

totally understood. But purely from a battery science aspect, still curious as to whether charge/discharge cycles are any factor at all in longevity

Of course they are, but you don’t seem to be understanding the definition of a cycle.

A discharge from 100% to 0% is “one cycle”.

Five discharges from 90% to 70% is also “one cycle”.

Plug your car in, like Tesla tells you to. A higher number of shallow discharges is better than fewer large discharges.

 

[tnt1971]

If you want to baby it, don't charge it over 70% unless you need to. This is directly from Dahn, and he is Tesla's battery expert. The lower the SOC, the better, except if you go too low, like less than 10%-20%. I have heard that "depth of discharge", which is what you are getting at by talking cycles, is a factor as well. So swings of 10% are supposedly better than going from 90% to 10% and then recharging, but I have only heard this from forum members with no science behind it. I rarely do more than 50 miles in a day, and leave my car overnight in the 40-60% charge range.

I have seen conflicting information on fast charging and how it affects health. Some say not at all, others say it could be a problem, and Tesla dropped my supercharge rate with chargegate. When at home or work I charge at 32 amps or less (I have one of the older cars with the 40 amp onboard charger). The onboard chargers go after a time, and I have always thought it better not to use the max amps and run up the heat levels on it unless I am in a hurry, which is not often. I thought that would make it last longer. I have also done about 10 range charges in the 4.5 years of ownership and I never let it sit at the 100% charge level.

The results, my car had 275 miles new (it was rated at 270) and I now have 262 after just over 75,000 miles. My only service issues have been door handles and a loud AC fan motor that had to be fixed.

 

[beatle]

Since I've been driving the car a lot less (maybe twice a week) I charge to 75% and leave it plugged in. Any higher and the cooling pumps run and whine. If I am planning a slightly longer trip I charge to 90% right before heading out as the car has more power with a higher SoC.

If I were still commuting, I'd use scheduled departure. That leaves the battery at a lower SoC for the evening and then it only bumps back up to the max charge set (say 90%) right before you're ready to leave. I think this is probably better for the battery and it has the side benefit of adding a bit of heat into the pack which helps lower internal resistance and yielding slightly better efficiency. All of these may be pretty trivial changes, but they aren't inconvenient to implement.