James Broadhurst said:
Oh, come on, they are! They're defending themselves against guarantee claims; guarantees which they have to give otherwise no one would buy them.
I'm still interested in knowing how it's done. Occasionally I would have liked to put a half charge in 30 minutes but the speed with which the pack hits 4.2v is just too quick. The quicker I taper the current, the longer the charge takes.
Given a big enough charger, I can get a cell from empty to 4.2v in a matter of seconds, if not shorter. That doesn't mean it's 100% charged. That's just the voltage recorded at the charger, not the potential difference between the anode and cathode (which is again different from the voltage recorded at the cell ends).
So how do they do it? I don't know specifically, but here's my guess, since I see my EV charger occasionally dropping to 0W for a few seconds to a few minutes - They set a CC-CV charge method with two profiles - one with a high constant current when the SoC is < 50%, and one with a low current when the SoC is > 50%.
At first, they just set high constant current. The voltage will slowly rise, but it's ignored unless it hits 4.2v per cell. During the CC phase, voltage is not a reliable indicator of State of Charge. Once the battery is charged enough to hit 4.2v per cell, they go constant voltage instead, and the cell controls how much current is absorbed. Again, voltage is NOT a reliable indicator of State of Charge, because it's affected by the internal resistance of the cell.
Every <X> minutes, they disconnect the charger for a few seconds, and sees where the voltage settles to. THAT is the accurate measure of state of charge. Once that "settled" voltage indicates cells are >50% SoC, they probably do a much slower constant current charge to protect the battery.