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Charging at 1/2, better or worse for battery life?

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Many days I have the option to charge or not charge the car when its around 1/2 (~100 miles on my 60kWh). I know the next day I'll probably only need 20-30 miles at most.

I'm wondering if its better for battery life to let it get very low (20-30 miles remaining) or charge it back to full when its around 1/2 ...or does it make no difference?

(The one reason I do charge it to full is for better acceleration :p)
 
Li Batteries should be charged as often as possible. Battery deterioration occurs because the graphite anodes in the battery physically swell up and shrink as they absorb and release electrons. It is this shrinking that causes microcracks and reduces capacity. So yes, as apacheguy has already stated, the charge cycles should be kept as shallow as possible.

It's similar to the human body: You can gain and lose five pounds of bodyweight ten times in a row and will be none the worse for wear, but gain 50 pounds and lose them again all at once and you will be left with stretch marks and flabby skin.
 
Ok.

I do public charge whenever I can but try not to charge at my house if I can avoid it (costs more even in off peak!)

I understand the "cost" of power at home. Still plug in your car at home to 120V outlet and just reduce the charging rate to 2 amps/hour rate. Save money versus 12 amps per hour. You still have your car plugged in. It is a pittance of a charge rate, but it "protects" your battery by having some power going into the battery. It is only about a .1 to .2 kWh.

I am curious, what do you pay for kWh? High and low.
 
I understand the "cost" of power at home. Still plug in your car at home to 120V outlet and just reduce the charging rate to 2 amps/hour rate. Save money versus 12 amps per hour. You still have your car plugged in. It is a pittance of a charge rate, but it "protects" your battery by having some power going into the battery. It is only about a .1 to .2 kWh.

Charging at low amperate rates will probably cost you more at the meter since the coolant pumps and battery thermal management system may continue to run the entire time (also shortening their life). I believe there were some studies in the Roadster forum that show that charging at less than 20A on 240V lowers efficiency significantly. I charge at 20 or 30A (240V) and never do 100% range charging unless absolutely needed. #1 Enemy of LiIon battery is prolonged exposure to high heat. (Refer to Leaf battery degredation reports from Phoenix; however, unlike the Teslas, Leaf batteries don't have protective active cooling.)

Prolonged SOC at 100% also shortens life; I wonder which is worst: 100% SOC state for long periods, or long periods at very low SOC. The car is set to keep the SOC in the 85 to 90% range since it will top off once a day when idle, after losing a few % of range. I assume Tesla figures this maximizes battery life as well as insuring that when you jump in the car you still have adequate range. So I just leave mine plugged in and let the management system take care of the periodic top-offs. If I need to leave it unplugged, I don't get too excited unless it starts to run into to a stretch of several days w/o a top-off.

If I just run to the store and only use a couple of miles but plan to drive later, I don't bother plugging in either. But, if the SOC is less than 50%, I always plug in as soon as possible. (I estimate SOC by assuming 100% = about 300 ideal miles, so 50% is at about 150 ideal miles.)
 
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Tesla states to always keep the car plugged in. The HV battery is always at 85% charge if you select standard charge. I treat my MS like any other car. I don't worry about SOC. I just keep it plugged in. I try not to out think the engineers who built the car. The engineers know so much more about the car and how to keep it in the best possible condition. Similar to keeping the ICE oil level between low and full. I don't adjust the oil level based upon what I think is best, I just do what the manufacturer tells me to do.
 
Tesla states to always keep the car plugged in. The HV battery is always at 85% charge if you select standard charge. I treat my MS like any other car. I don't worry about SOC. I just keep it plugged in. I try not to out think the engineers who built the car. The engineers know so much more about the car and how to keep it in the best possible condition. Similar to keeping the ICE oil level between low and full. I don't adjust the oil level based upon what I think is best, I just do what the manufacturer tells me to do.

How does this discussion change if you have timed charging on a TOU rate? Does the Model S still draw a slight charge outside of the timing window?


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I understand the "cost" of power at home. Still plug in your car at home to 120V outlet and just reduce the charging rate to 2 amps/hour rate. Save money versus 12 amps per hour. You still have your car plugged in. It is a pittance of a charge rate, but it "protects" your battery by having some power going into the battery. It is only about a .1 to .2 kWh.

I am curious, what do you pay for kWh? High and low.

haha... well, winter isn't 'too bad'

For March i am paying $0.226 average (1446 kW)

winter - partial peak baseline - $0.12 off peak - $0.10495
> 200% - $0.32945 -$0.3131

summer - peak baseline - $0.10070 partial peak -$0.17528 peak - $0.2872
> 200% - $0.2872 -$0.38343 - $0.49535

so 1$ ( with $0.25 back from Chargepoint for each session) per 6.3 kW is a pretty good deal - especially in summer + I get a nice walk


and wrt to the trickle charge, I did the slow trickle a couple of times at first but I think the best charge technique is right before driving in the morning since it warms the car a bit while it is charging + regen is fully active when the temps are low.
 
haha... well, winter isn't 'too bad'

Darn, you pay some serious money for electricity!!! So, Chargepoint is much better deal. How far away is it???

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How does this discussion change if you have timed charging on a TOU rate? Does the Model S still draw a slight charge outside of the timing window?

I have not seen it draw any power outside of the timing window. If it does, it is very slight.
 
We who live in The People's Republic of California (Northern on Pacific Gas & Electric) are so used to getting ripped on our utility rates we are numbed to the effect on our wallets. During peak hours using Rate Schedule E-9 designed for EVs, over 300% of Baseline usage is at a laughingly low $0.58583/ kWh. On Rate Schedule E-6 rates go as high as $0.48653.
 
We who live in The People's Republic of California (Northern on Pacific Gas & Electric) are so used to getting ripped on our utility rates we are numbed to the effect on our wallets. During peak hours using Rate Schedule E-9 designed for EVs, over 300% of Baseline usage is at a laughingly low $0.58583/ kWh. On Rate Schedule E-6 rates go as high as $0.48653.

Agreed. I've been charging at public chargepoints that are 1 block from my condo for $1/hr, which works out to be about 16cents/kwh flat rate.
 
I understand the "cost" of power at home. Still plug in your car at home to 120V outlet and just reduce the charging rate to 2 amps/hour rate. Save money versus 12 amps per hour. You still have your car plugged in. It is a pittance of a charge rate, but it "protects" your battery by having some power going into the battery. It is only about a .1 to .2 kWh.

Yes but this seems like a bit "too much". How about having it just plugged in when you get home every day and have it charge at off peak times. Lets say someone gets home at 5pm, charges for a while on 110V or 5A on their 220, then sets the charge up again at 10pm at 40A? will they really be saving that much of the battery?

Or will this kind of effort only apply when you return home and your battery is quite low? Say 50% or lower.

but if you did a typical short trip of up to 30 miles, just wait till off peak hours?
 
As long as you stay away from keeping the pack at or near 100% SOC for long periods of time, the SOC doesn't have a have a huge effect (diminishing returns). Like others have said shallow cycles are better.
 
We who live in The People's Republic of California (Northern on Pacific Gas & Electric) are so used to getting ripped on our utility rates we are numbed to the effect on our wallets. During peak hours using Rate Schedule E-9 designed for EVs, over 300% of Baseline usage is at a laughingly low $0.58583/ kWh. On Rate Schedule E-6 rates go as high as $0.48653.

Bleah! At those prices it's much cheaper to put up your own solar panels to generate your own electricity!

Out here in the land of 11 cent hydroelectricity it hasn't seemed worth it.