HardDrives either work or fail they rarely deteriorate. Either the platters, (where the data is stored) or the controller circuit board fail. There is little chance of recovery from either of these failures.
I carry two identical mains powered external hard drives to very gig. It takes moments to swap out the hard drive and power supply in the event of malfunction.
Happened to me once, hopefully if it happens again I will be ready.
Non powered drives take their power through the usb connection of the laptop. IMO they are suitable for small transfers of data but NOT suitable for continual access. Too much strain on the usb bus bar.