Not all of the cells give up energy / charge at exactly the same rate, so at the moment you stop driving there could be some energy imbalance.
Imbalance is caused by the initial energy capacity of a brick being lower (imagine a brick with 45 cells in parallel rather than 46). Roughly speaking, the bricks will discharge energy at the same rate (though not exactly the same rate, as current will be necessarily the same in each brick, but brick voltages will deviate over time during the discharge event). The brick imbalance (as I understand it) is really a voltage imbalance caused by initial energy content differences (and the imbalance I think can occur after both discharge and recharging events). There are a lot of possible scenarios. But in a simplistic case, I believe your battery capacity at 100% is approximately limited by the energy content of your minimum energy brick (since it will become empty first (since energy discharge rate is roughly the same for all bricks), and all bricks discharge in series so there is no way to extract the energy from the other bricks (caveat: that is the case without some downtime to somehow rebalance, but I think rebalancing is only a thing done at high SoC (above 90%), not low SoC - don’t think there is a provision to transfer energy from a healthy brick to a weak brick at
low SoC - my understanding is rebalancing is done at high SoC by bleeding down (wasting energy) the (usually?) lowest capacity, highest voltage brick, so that charging of all other stronger (lower voltage at that instant) bricks can continue (resulting in a higher overall pack voltage after a subsequent top-up charge, which of course maximizes energy available)). But that weak brick will still be the limit during a discharge. But the “area under the curve” will be higher since you start with a higher pack voltage than you would have without rebalancing, after the top up. The CAC (calculated Amp-hour capacity) is a measure of the amp-hour capacity of that worst brick. But the energy available can be improved by other healthy bricks - since a healthy brick reduces its voltage slightly more slowly during a discharge than a weaker brick (for an identical current draw), the pack voltage will be higher for the discharge period after a rebalance, meaning there is more energy under the I*V Vs. time curve (power integrated over time is energy).
Does anyone ever actually check there range by running the car until the battery is at 0%? Of course not.
I’m not sure why we keep coming back to this. People do discharges to 5% all the time on road trips, and this is plenty to notice what is your range! Loss of capacity (which is real!) happens, and matters! How much? Not much. I’ve lost a true 10% capacity (287 rated miles, 70.3kWh, vs 78kWh (over 310 rated miles when using the same energy content per rated miles but rated miles are initially swollen to minimize customer consternation and to allow everyone to have 310 (pre-2020) rated miles when new, even if the energy contents of different brand-new packs differed by 1-2kWh. ) Do I notice loss of capacity? Sure. I can’t make certain stretches to Superchargers that I could have made before. Does it matter? Not too much at all, as long as Superchargers are spaced sufficiently closely. Slightly longer waits at Superchargers are needed to make the same legs now.
But loss of capacity is real; people measure it accurately all the time (either through a discharge monitor, or a charging event measurement). This is not something we need to continue to debate. It happens (to everyone!!!), it's normal, and it's fine (unless it's excessive).
