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battery lifetime

Discussion in 'Battery Discussion' started by Eumox, Jan 4, 2010.

  1. Eumox

    Eumox Member

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    I just registered to this forum to find out if anybody has long-term experience with the Tesla Roadster.
    Personally I never encountered any electrical device with Li-I batteries that kept its quality for more than a few years. All my laptops worked for 3 hours at the beginning and (now at age 3 to 4 years) only for about 1 hour , my robotic vacuum cleaner could go for 40min before recharging and now (after 3 years) only 20 min.
    I suppose that someone who can afford a Roadster can also afford new batteries (worth 60k USD) after 4 years.
    Model S owners will probalby have a problem with paying another -say 30k USD after 4 years.
    What do you think?
     
  2. qwk

    qwk Model S P2681

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    First of all, the roadster battery is nowhere near 60k.

    Secondly, they have a 4 year warranty.

    You can't compare a $100 laptop battery, to a Tesla battery pack that is water cooled and precisely computer controlled.
     
  3. mpt

    mpt Electrics are back

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    We're all taking a gamble here, but a reasonable one. I don't know of anyone that has long term experience though Tesla did trial the packs as part of the testing.

    The things that traditionally kill Li-on batteries; heat, excess charge or discharge, cold charging, etc. are managed in the Roadster; check out the battery discussions around the site; there is much discussion as you can imagine.

    Tesla warrent the battery for three years but will go longer for extra cash and will offer to allow you to pre-purchase the replacement for $12,000.

    I suspect that many of us anticipate some expense after five years but all anticipate replacing the pack with a cheaper, lighter and longer lasting pack. There's already talk of nearly twice the original capacity.

    Interestingly, the Volt, as a plug in hybrid, has to have a battery that lasts ten years by law in the USA. To acheive this the Volt has a 16KWh battery that is only used as an 8KWh unit; GM says that their battery will last ten years but will drop 50% in capacity.
     
  4. Eumox

    Eumox Member

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    @MPT: That sounds reassuring. That's actually the best news I heard (during all my research about this dream car :).
     
  5. mt2

    mt2 Member

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    You may also want to extend your research to the Tesla Motors Engineering blog. I can't find one single post that sums up all the battery technology - but I only skimmed. Here are a few that discuss different aspects of the technology, Tesla Motors - Engineering.

    In short
    * The batteries are maintained within a certain temperature range.
    * Coolant distributes the heat so cells age at the same rate across the pack.
    * Charging is limited to 90% of capacity.
    * Discharging is limited to 10% of capacity.
    * And a lot of other proprietary stuff I either don't understand or are not privy to.

    To a large extent, the battery technology is Tesla's "special sauce", which is why they are also in the business of selling the drive train to other manufacturers.

    That's just a general layman's understanding. Roadster owners and electrical engineers can elaborate - and have in the various threads here.
     
  6. TEG

    TEG TMC Moderator

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    The PEM will cut power drain from the battery pack at times when it thinks it could damage it. There are basically all sorts of safety and longevity subroutines available to come into play when needed. Sometimes it might have been nice to have them more gradual and blended rather than "Jekyll and Hyde" personalities that can happen if you try to over-bake something.
     
  7. Eumox

    Eumox Member

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    It's great how you guys sum up the facts for my easy understanding.
    Encouraged by this I would like to ask for your opinion on the latest entry from the roadtrip:

    2) If my drivers keep my battery warm, I have no problem waking up in the morning. Even if I’m cold when I start, I have no problems getting going. To protect my battery life, my battery needs to be a certain temperature when charging. On this trip, despite the cold temperatures, this hasn’t been a problem because my drivers plug me in when we’re not on the road.

    Does this mean that the batteries are water cooled but need to be garage warmed for charging?
     
  8. mpt

    mpt Electrics are back

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    The batteries are, as MT2 puts it; maintained within a certain temperature range.

    The car doesn't need to be garaged but, when you charge, if the cells are too cold or too hot the car will begin by heating or cooling the cell pack first.

    The car will drive when the batteries are too cold to charge or too hot for proper operation, performance is slightly reduced on the limit and there is no regen braking when cold. The battery naturally warms up (self heats) in use so regen can and usually returns after some driving.

    It takes many many hours at sub-freezing temperatures to cool the pack to the point where it won't charge; at -8C I didn't use the car for a few days and the pack had cooled. After the first charge at 3am in the morning the pack heated and at 6am was still warm and fully operational despite the temperature falling to -9C.

    There is also a 'storage' mode to virtually suspend battery aging when the car is left for weeks at a time without planned use beyond a few short trips, say 10 miles a day. In this mode the charge is allowed to fall to 20% where, li-ion technology will last forever (ish). Apparently, to make li-ion actually last forever, a 20% charge on cells stored at -4c is the ticket, so I suppose there is some merit to keeping your car outside.

    In short, it's just plug-n-play simple but remember to add up to an hour to the charge time if the pack is very cold but who cares when it's outside and you're warm and toasty in bed.
     
  9. Palpatine

    Palpatine Banned

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    #9 Palpatine, Jan 10, 2010
    Last edited: Jan 10, 2010
    Also most people will be doing a deep discharge cycle every day on the Volt battery pack cells. With only 40 miles of range, they will be used much more often to their full depth of discharge.

    With my Tesla and the 200 mile range, it is very rare for me to go below 50% on the battery pack. If we assume that "standard" takes the cells to 80%, then most Tesla owners are between 50% to 80% on their battery pack just about every day. That is very gentle charge/discharge on the cells.

    That is something Elon Musk pointed out for why Tesla rejected building a plug-in hybrid like the Volt. The larger battery pack of a pure EV is much more simple and reliable long term.
     
  10. tennis_trs

    tennis_trs 2010 2.0 Roadster Sport

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    The only percentage I remember seeing indicated by Tesla for the Storage Mode charge is 50% SOC with just 40% available unless/until switching to Range Mode to get access to the final 10%. The place I saw this was on a sheet of paper, titled "Tesla Roadster Battery Modes", which came with the car. I looked again at the soft copies of the manuals and none seems to indicate what this percentage is.

    Has anyone seen other values documented?

    What have people who've used Storage Mode seen? Maybe I'll try it some when I expect to not need near 20% on some days.
     

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