Lately, there seems to be a trend in cell phones where they have 2 separate batteries, and this is claimed to increase changing speed. See "Oppo suggests that because the two batteries can be charged at once, charging can go faster than if the device only used one unit." And "With this new setup, both batteries can charge at more than 30W simultaneously while staying cool even when using the phone,"
As I understand it, lithium batteries have charge rate typically defined in C, where C is the capacity. For ex. a 4Ah battery with a 2C charge rate can charge at 8A. This leads to the idea that the battery charge time is 1/C hrs (ignoring the constant voltage segment at the end).
With this understanding, splitting the battery into 2 cells shouldn't increase charge speed at all. Is there some electrochemistry explanation I'm missing for why smaller capacity cells have higher charge rates?