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Tested charging warmer battery

Discussion in 'Model 3: Battery & Charging' started by surfrasch, Dec 29, 2019.

  1. surfrasch

    surfrasch Member

    Joined:
    Oct 14, 2018
    Messages:
    330
    Location:
    Hollis, NH
    in NH, car has 16k miles on it, theoretical range dropped at V10 early October like most everyone whining on the forum. Mine didn't drop that badly....it was historically consistent 310 at full charge, dropped first to 308 after V10 (the next day), then 307, continuing down to 303 two weeks ago. Okay I wasn't worried, just rolled with it and kept reading from the experts on the forum here, appreciated all the insight.

    Anyhow someone mentioned here that the battery won't charge to 100% when cold, because when the battery warms up there is expansion involved so the system automatically limits how high a cold battery can charge. I tested this out yesterday, and now I get it. We had to charge to full yesterday for a brief trip, we were leaving the house around noon.

    Overnight car was charged to roughly 245 miles, close to 80% estimate.....my normal level (used to be 250 miles pre V10).
    at 7am (temp outside around 32F, warmer in garage) I jacked the charge up to 285 miles, that took a bit over an hour with my garage Tesla charger at 240V
    after this reached 285, I took the car out running errands for an hour, then returned to the house
    increased charger set point up to 100% charge, and it charged to 309 miles rated range.

    That's the highest I've seen since early October. Conclusion, temperature of battery is a larger factor than I had imagined when charging to 100%. I still think something changed with V10, but I'm not going to worry about.....just drive my car and be happy.
     
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  2. AlanSubie4Life

    AlanSubie4Life Efficiency Obsessed Member

    Joined:
    Oct 22, 2018
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    8,673
    Location:
    San Diego
    I don’t think that’s quite true. Cold simply means your “fullkWh” is reduced. The battery will still charge to 100%. That 100% is just different than a warm 100%.

    If you can, take that car at 309 miles and park it outside overnight. I think you’ll find it is below 303 in the morning. It’ll look like excess vampire drain but you’ll see the battery is still at 99% or so even if you have lost 8-10 miles.

    Leaving it at 309 overnight in cold weather likely won’t hurt it but best not to leave at 100% too long. You can do the same experiment just charging a warm battery to 90% though...leave that car outside in the cold overnight (it needs to be quite chilly and you need to leave it long enough) and it will be at 89-90% with something like 7-10 fewer miles available the next morning.
     
  3. surfrasch

    surfrasch Member

    Joined:
    Oct 14, 2018
    Messages:
    330
    Location:
    Hollis, NH
    thanks.....ok, not sure I understand this.....how could a warm 100% be a different range measurement than a cold 100%, if the range measurement is based on the standard W/mile government rating and the kWh energy capacity of my battery pack?

    hey still learning, it's all very interesting to me.....
     
  4. DickBlonov

    DickBlonov Member

    Joined:
    Aug 15, 2019
    Messages:
    31
    Location:
    Montreal
    The rated capacity of any battery is specified at a certain temperature. Change the temperature, the capacity changes.


    Phil
     

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