TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

Model S battery Life Cycle Exercise

Discussion in 'Model S: Battery & Charging' started by scaesare, Sep 22, 2014.

  1. scaesare

    scaesare Active Member

    Joined:
    Mar 14, 2013
    Messages:
    3,940
    Location:
    NoVA
    #1 scaesare, Sep 22, 2014
    Last edited: Sep 23, 2014
    With another couple of "high profile" threads highlighting the issues with battery degradation, as well as the advances in battery chemistry between the Roadster and the Model S, I got to thinking about expected battery life for my circumstances.

    It's been suggested (bothe here, and in various whitepapers and articles by Tesla and others), that the Roadster used earlier Li-ion technology (Li-Ni?) that would be good for ~500 full discharge cycles before having degraded to a specific point (70%).

    The Model S has a newer chemistry (NCA?) that has rumored to be good for 2,000+ cycles to get to the same point.

    As the rating is based on full discharge cycles, it's understood that two 50% discharge cycles is equivalent to a full cycle (more or less)... and is the same for four 25% cycles, etc... It's also understood that those shallower cycles in the "middle" of the charge range is better than extremes at the top or bottom of the range.

    So, I'm almost exactly at 2,000 miles a month on my S85. That averages to 67 miles a day over 30 days. It just so happens my weekday commute is about 66 miles. Apparently my weekend driving keeps up this average pretty closely.

    That's also just almost exactly 1/4 the range of a full charge. Which matches my typical charge at night I charge to 60% and typically plug in around 35% at night... or about 25% of charge I add nightly on average.

    So... if the expected pack life is 2,000 full cycles, I could be looking at 8,000 of my average nightly charge to reach the same point. That's 22 years.

    Now, I don't expect I wont see degradation before then... as there are ather factors such as just calendar age, etc... but as long as the thermal management of the car is doing what it should it will be interesting to see how well our packs retain capacity over time...
     
  2. Chris TX

    Chris TX Active Member

    Joined:
    Sep 30, 2013
    Messages:
    1,486
    Location:
    Dallas, TX
    FFS, I'm a bit tired of seeing some guy's Roadster battery woes on EVERY social media outlet known to man. "Maybe if I complain hard enough, Tesla will give me a new battery so I'll shut up" seems to be the common thought amongst my immediate circle of EV minded friends. This really isn't helping the EV cause at all but hey, if that guy gets his Roadster pack fixed, good for him! /sarcasm

    I've got ~15k miles on my 10 month old S85. I've had maybe 20 top offs (max range) and ran it down to "Charge Now!" about 5 times. I still have 235.65 miles of Standard Charge and that's actually 1 mile more than when I first got the car (firmware display might be responsible). I expect some degradation over the next few years, but it I was told about this before I even put down a deposit. Ask me in 4-5 years what my Standard range is, and we'll see what's changed. ;)
     
  3. scaesare

    scaesare Active Member

    Joined:
    Mar 14, 2013
    Messages:
    3,940
    Location:
    NoVA
    I tend to agree... but the other couple of threads are sufficient for that issue... I rather hope this one might discuss what reasonable expectations for the Model S pack are...
     
  4. Lloyd

    Lloyd Active Member

    Joined:
    Jan 12, 2011
    Messages:
    4,886
    Location:
    San Luis Obispo, CA
    I expect to be at ~70% or better at the equivalent of 3000 full charge and discharge cycles. That is a lot of miles!!
     
  5. scaesare

    scaesare Active Member

    Joined:
    Mar 14, 2013
    Messages:
    3,940
    Location:
    NoVA
    Something like 650,000 miles....
     
  6. rdrcrmatt

    rdrcrmatt Member

    Joined:
    Jun 27, 2013
    Messages:
    551
    Location:
    Milwaukee
    I'm still seeing 225-231 miles on 90% charge, 255-260 on 100% charge.. just over a year old, 41,000 miles.

    I drive 160-240 miles per day when I have my long commute (3-4 days per week)

    Mileage * Wh/Mi Avg / kilo / usable kwhr in battery
    41000 * 330wh/mi / 1000 / 75 = 180.4

    That's 180 "full" charge cycles so far. So at "2000 charge cycle life" I'm nearing 10% used in my battery. So, 400,000 miles for me to hit 2000 charge cycles or that 70% point.
     
  7. Lloyd

    Lloyd Active Member

    Joined:
    Jan 12, 2011
    Messages:
    4,886
    Location:
    San Luis Obispo, CA
    Remember that the degradation curves showed more degradation the first year, then tapering to about 1% per year IIRC. ~265 is what most see after new, so that would be about a 4% degradation after your use.
     
  8. scaesare

    scaesare Active Member

    Joined:
    Mar 14, 2013
    Messages:
    3,940
    Location:
    NoVA
    As Lloyd points out, the curve is non-linear... I don't have exact numbers, but I think I probably lost something like 3-4% in the first 4-6 months... and I'm not sure I've seen much more since then (although I rarely range charge and thus I'm not sure what my max is, nor am I sure I don't have some pack imbalance).

    But there's something odd about your numbers. If you drove your average commute only 3 days a week for a year, you'd have about 90K miles, no?
     
  9. bemental

    bemental Member

    Joined:
    Sep 21, 2014
    Messages:
    11
    Location:
    Maine, USA
    I remember reading about Tesla's battery swap option (instead of a charging), and I believe we will be able to keep the battery that we exchange for instead of picking our old one, to the effect of a small fee if the replacement battery is newer then the replaced.

    In theory, this should reduce anxieties associated with battery degradation, but may end up feeling more like a crap shoot akin to buying a lease or loaner car from a dealer.
     
  10. yobigd20

    yobigd20 Well-Known Member

    Joined:
    Oct 28, 2012
    Messages:
    5,793
    Location:
    Skaneateles, NY
    you are completely wrong in your understanding. two 50% discharge cycles are NOT EQUIVALENT to a full cycle. You might get the same range out of that, as well as the same range from four 25% cycles, but definitely NOT EQUIVALENT to a full cycle with regards to battery capacity longevity. The shallower the discharge cycles, the less 'damage' will occur to the battery, thus extending its life. so if you were to compare somebody that does 100% discharge cycles only and drove 132,500 miles (265*500), that battery pack might have (making this number up) 80% battery capacity remaining. comparing that to someone who did 1000 50% discharge cycles and for a total same amount of mileage 132,500 miles (132.5*1000), that battery pack might have 90% battery capacity remaining. comparing that to someone who did 2000 25% discharge cycles and for a total the same amount of mileage 132,500 miles (66.25*2000), that battery pack might have 95% battery capacity remaining. you see the difference? the shallower the cycles, the less damage occurs to the battery cells resulting in a really long battery life. theoretically if you only drive ~2.65 miles round trip daily and limited your discharge cycle to 1%, your battery pack might go 2093509327509237 miles before it's down to 80% capacity. (numbers are made up solely to prove the point that two 50% discharge cycles are NOT EQUIVALENT to a full cycle and so on for shallower cycles). fyi this is why Tesla also repeatedly states to charge as often as possible - plug in every night. that limits the discharge depth and thus increases the battery capacity longevity.
     
  11. brianman

    brianman Burrito Founder

    Joined:
    Nov 10, 2011
    Messages:
    15,487
    In this context, what do you consider a "small fee"?
     
  12. yobigd20

    yobigd20 Well-Known Member

    Joined:
    Oct 28, 2012
    Messages:
    5,793
    Location:
    Skaneateles, NY
    original.jpg
     
  13. scaesare

    scaesare Active Member

    Joined:
    Mar 14, 2013
    Messages:
    3,940
    Location:
    NoVA
    #13 scaesare, Sep 23, 2014
    Last edited: Sep 23, 2014
    There certainly are additional factors, (hence my use of "more or less equivalent), but look at the typical battery life as a function of Depth of Discharge (DoD):

    dc.PNG
    Table 2 compares the number of discharge/charge cycles Li-ion can deliver at various DoD levels before the battery capacity drops to 70 percent. The number of discharge cycles depends on many conditions and includes charge voltage, temperature and load currents. Not all Li-ion systems behave the same.

    You'll see that there's roughly an inversely proportional relationship between DoD and # of cycles.

    If you want to learn at some of the other factors, there's a good discussion at Battery University
     
  14. bemental

    bemental Member

    Joined:
    Sep 21, 2014
    Messages:
    11
    Location:
    Maine, USA
    Perhaps I should have used the word nominal, instead of small, but if I would be able to exchange my aging battery pack for a newer one for $500-$1000, I'd consider that a deal.
     
  15. rdrcrmatt

    rdrcrmatt Member

    Joined:
    Jun 27, 2013
    Messages:
    551
    Location:
    Milwaukee

    you're right.. I forgot that I didn't drive it much last winter as the commute was just a bit out of reach for the battery in the very cold weather we had.

    I'd say I averaged 3x/week, some more, some less, from July 2013 - June 2014 it was 2-3x /wk 180-200 miles round trip.. since end of july it has been 145 round trip 5x week.

    minus the time the car wasn't used for the commute (was used for around town trips) and we get the mileage I'm at.
     
  16. scaesare

    scaesare Active Member

    Joined:
    Mar 14, 2013
    Messages:
    3,940
    Location:
    NoVA
    Cool. That's a pretty steep commute! I suspect your mileage will put you at the higher end of the range so it will be interesting to see how your pack fares...
     
  17. omgwtfbyobbq

    omgwtfbyobbq Member

    Joined:
    Aug 24, 2013
    Messages:
    460
    Location:
    Southern California
    NCA capacity seems to largely be a function of average temperature versus SOC and depth of discharge rather than energy stored (cycles).

    http://www.nrel.gov/vehiclesandfuels/energystorage/pdfs/45048.pdf (Page 18)

    What's really interesting is that 4 cycles/day is pretty much identical to 1 cycle/day. In that context, I'd drive it like I stole it, or at least like a cab driver.

    With that said, production Li cells are relatively new and haven't been tested in real world conditions, so who knows what pack life will be. To further complicate things, with 7000+ cells, variability in manufacturing can impact pack life substantially.

    I think it'll be good in the aggregate, and great for people who drive a lot. But the flip side may be that the pack's calendar life could be the biggest limitation, especially in warm environments, and that there may be variances in manufacturing that won't pop up until after the warranty period.
     
  18. Rothgar

    Rothgar New Member

    Joined:
    Oct 1, 2014
    Messages:
    4
    Location:
    Georgia
    This is great! I came to the same conclusion in regards to my recharging profile...my round trip daily commute is 64 miles, so I set it at 60% just a you do. My reasoning was the same as yours. Thanks!
     

Share This Page