If the battery in the laptop is still good, it comes with it's own UPS. My MBPs haven't had an ethernet port in a minute, so do you have to supply your own adapters as well??? You could fit ~15 MBPs on their edge in 9RUs. That'd be an interesting looking rack. Not quite a blade chassis. It'd be rather boring looking as there's no blinky-blinkies

Putting a UPS in a rack is a prosumer/corporate IT thing, it’s not done in real datacenters.

They typically have their own UPS in another room and multiple power lanes. And it’s going to be much more reliable than a laptop battery.