Charge level

The general rule is that the lower the state of charge, the longer the battery will last. If you only need 40 miles per day you can just charge to 50% and be totally fine in terms of range. But it's reasonable to charge a little higher to give you some buffer in case you need to drive more. In your case I'd probably go to 60 or 70%. I think you don't have to be too concerned about battery life as long as you stay mostly below 80%. Charging to 90 or 100% isn't bad if you start driving right away. The factor is time. If you charge it to 100% and let it sit like it for a long time, that would be bad.

I don't have the reference handy, but someone once tweeted Elon something along the lines of: "If I only need 20% of the battery per day, is is better to charge to 60% (keeping the battery in 40%-60%) or 90% (keeping the battery in 70%-90%)." Elon replied with "40%-60%".

In the long run, keeping the SOC averaged around 50% is best, but the impact on the battery keeping it in the 70%-90% range is pretty minimal.

tga said:

I don't have the reference handy, but someone once tweeted Elon something along the lines of: "If I only need 20% of the battery per day, is is better to charge to 60% (keeping the battery in 40%-60%) or 90% (keeping the battery in 70%-90%)." Elon replied with "40%-60%".

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Here's the actual tweet:

Mats Remman @cairnz
@elonmusk My daily commute takes about 50% SOC. What would be best for the battery long term.. 90%->40% charge daily, or 80%->30% ? (85kWh)
25 March 2014

Elon Musk @elonmusk
@cairnz 80% to 30%
25 March 2014

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Low SOC, cool temperatures and shallow depth of discharge all help extend the life of Li-ion batteries.

djp said:

Here's the actual tweet

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Thanks for looking it up.

The Chevy Volt is "88% -> 23%", I take that as a hint that doing 70% -> 40% will work great - essentially charge such as the battery median charge is between 50% and 60%

So then on a long trip, say cross country, can one always charge to 100% and hit the road as soon as possible, if you think you may need the max range?

cottylowry said:

So then on a long trip, say cross country, can one always charge to 100% and hit the road as soon as possible, if you think you may need the max range?

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Yes...