Charging Approach

[jerry33]

Even if you "only" get 1000 full cycles out of the battery before it's significantly degraded (or let's say 2000 half cycles) that's still going to be equivalent (with conservative estimates) to some 200k+ miles of driving (300k+ kilometers) which is quite a lot for any automobile. I would wager it would take most people at least 5 years to drive that ammount, for most a lot more (taxis being the exception) especially since EV's, even Model S, is not a good car for any setting where the car has to be on the road for more than 8 hours per day every day. For most I would assume it would take 7-8+ years to drive 200k miles, and at this point the car as a whole is starting to become worn, outdated and shelf-life (independent of use) starts to become an issue for the battery as well. So there is really no point in having habits that would allow for example 10000 cycles, since you're never going to need 10000 cycles anyway.

That might be true in Europe, it's certainly not true in North America. I expect cars to last 500,000 km at a minimum.

 

[Johan]

That might be true in Europe, it's certainly not true in North America. I expect cars to last 500,000 km at a minimum.

You're right of course, if the car is otherwise great I can see a lot of people driving it 500k+ km (here in Europe too). With an EV and with the current technology the battery is probably going to be the first "major" part of the car that needs replacement, especially since the drivetrain and motor seem very durable and there is no gear box. The battery has an ageing process which is happening in parallell with the usage wear but apparently these to forms of degradation are not additive but rather "whichever one is worse" (see this thread http://www.teslamotorsclub.com/showthread.php/10708-What-does-the-battery-degradation-curve-look-like for some very good discussion on the topic of battery degration).

If you plan on driving 500k km in say only 7 years (that's over 70000 km/year) then the degradation from use will be way more than "calendar degradation" (ageing) effects. If you do 500k km in 20 years of ownership (still 25000 km/year) then maybe calendar degradation is your biggest problem anyway, an effect that can't be remedied no matter what SOC you aim at keeping the battery at. So, if you're gonna drive 70k km per year that comes to 191 km every day (365 days a year). You're not gonna do that by charging to 50%! You will be using a lof of full charges and maybe also some range charges? And even if you're supercharging a lot you will depend on at least a full charge every night, right?

My point being that you can't both drive a lot while still using a charging scheme that keeps the battery a lof around 50% SOC - when you drive a lof you will often be doing near full cycles. Those who can follow the kinds of modified charging schemes described above are not the ones who will actually ever benefit from it while those who might actually have something to gain by it in theory can't do it in reality since they need to use the pack's full capacity for driving all those miles.

 

[jerry33]

You're right of course, if the car is otherwise great I can see a lot of people driving it 500k+ km (here in Europe too). With an EV and with the current technology the battery is probably going to be the first "major" part of the car that needs replacement, especially since the drivetrain and motor seem very durable and there is no gear box. The battery has an ageing process which is happening in parallell with the usage wear but apparently these to forms of degradation are not additive but rather "whichever one is worse" (see this thread http://www.teslamotorsclub.com/show...-does-the-battery-degradation-curve-look-like for some very good discussion on the topic of battery degration).

That's why you pre-pay for the second battery. Also as the Supercharger network gets built out, there will be less need to do range charges or run to empty.

 

[dtich]

posting a reply from tm engineering, no info really, but thought others would be interested in their response to my enquiry about various charging thresholds for the battery pack:

At the moment Tesla does not publish the thresholds for various battery behavior. As we gather more information about how exactly customers use their vehicles and the environments that they live in these sort of thresholds are fine tuned over time through software updates.

 

[100thMonkey]

I should have mentioned that I currently tend to leave the Leaf sitting at around 50% and charge up just prior to taking off the next time. I've gotten pretty good a gauging how much extra I need to charge the car to have it land me back at home around 50%.

Sure batteries will last longer in storage if they are at 50%, but these batteries are not in storage. They're being used - drawing power from them below 50% is harder on them. So it's not at all apparent that keeping the batteries at a lower SOC is actually good for the health of the pack.

 

[efxjim]

I imagine a used 85 pack would have some value as a "new" 60 or 40 pack for someone who has used up their 60 or 40 pack.

 

[100thMonkey]

I should say that my motivation for taking extra good care of the battery is not just to improve overall life but also to maintain maximum performance. they may sound like the same thing, but I like the batteries in all my devices to be in tip top shape so that when I need to, I can get the maximum "range" out of them. For instance, I have an ipad that is a few years old, I charge it when it hits around 40% and unplug it when it's around 80%, I rarely charge it to 100% and try and avoid leaving it for long periods at a high SOC. I rarely need to have it work like new, but on occasion, we go on long road trips where it's not unusual for the kids to watch movies on it all day, still, on a single full charge. With the S, if I could determine that there was a way to manage the battery to maintain maximum range for long road trips, I think it could be worth it. how many cycles the battery will last is one thing, how long it will maintain a like new capacity if treated well is yet another. we'll see what happens when we actually have the car and drive it for a while, we may just decide to not sweat it and stick with the Tesla protocol of charging every night.

Even if you "only" get 1000 full cycles out of the battery before it's significantly degraded (or let's say 2000 half cycles) that's still going to be equivalent (with conservative estimates) to some 200k+ miles of driving (300k+ kilometers) which is quite a lot for any automobile. I would wager it would take most people at least 5 years to drive that ammount, for most a lot more (taxis being the exception) especially since EV's, even Model S, is not a good car for any setting where the car has to be on the road for more than 8 hours per day every day. For most I would assume it would take 7-8+ years to drive 200k miles, and at this point the car as a whole is starting to become worn, outdated and shelf-life (independent of use) starts to become an issue for the battery as well. So there is really no point in having habits that would allow for example 10000 cycles, since you're never going to need 10000 cycles anyway.

The one thing I guess you could really do to hurt your battery with Tesla's current system is to consistently do range charges.

 

[Brian H]

I imagine a used 85 pack would have some value as a "new" 60 or 40 pack for someone who has used up their 60 or 40 pack.

Yes, especially since the degradation "flattens" -- it's mostly at the front end.