I use three - one stays on my desk, and the other two are in a rotation so there is always a fully charged one in my computer bag. All three are 8-15k mAh, as I find bigger ones unwieldy. The only one with PD delivery is my newest - the Aukey Sprint Wireless I reviewed here when this forum was starting.
My wife uses two - one lipstick tube sized that is always in her purse, and a slightly larger one for longer times away. One about 3500 mAh, and the other closer to 7000. She occasionally steals one of my bigger ones if hers is discharged or it will be an extended trip.
Besides those, I have one in a drawer at home for the kids to use when they need one - so 6 total.
Part of the reason I have this many is that they keep everyone happy and quiet on long car trips when everyone wants to be on their own devices, and there are only so many accesible car charger ports - the middle row of the van is a no man’s land for power outlets, and access in the back row is limited to one side. All of my kids use “hand me down” devices for their entertainment, which work fine for playing games long after their batteries stop lasting a reasonable amount of time. So they are effectively attached to a charging port for extended use. Most of the batteries have at least two charging ports, but sharing is hard, and cables get tangled, so one per person works best. My Aukey 6 port charger works great for getting everything charged again once we arrive at our destination.
I have had more over the years, tend to give them away when I get something better. The giveaway box currently contains one I got from some training along the way, but I don’t count things in that box as still being mine.