You speak in hypotheticals, but these things already exist. I often charge my car while shopping. The grid already handles high peaks. There's plenty of unused

You speak in hypotheticals, but these things already exist. I often charge my car while shopping. The grid already handles high peaks. There's plenty of unused capacity outside of the 6pm-10pm peak of the Duck Curve. Cars support scheduling charging, so even if you come home at 6pm and want to plug in without thinking about it, you can (and note that a modern BEV used for commuting needs to be plugged only once a week). If you charge at work, it's even better, because that's at the bottom of the Duck Curve when you could almost get paid to get the electricity off the grid. Fast DC charging sites often already have large battery storage built-in, because it's already more profitable to use lower-power grid connection and/or off-peak electricity.