SSDs do this exact same thing. The individual flash cells have much lower durability than the drive itself.
If you don't leave plenty of spare sectors over the very inevitable bad sectors will cause the drive to fail outright.
Perhaps that's a decision I'd like to make myself but it's still an essential function no matter what.
Leaving spare capacity in my battery isn't an essential function. That extra hundred or two miles the first few years of ownership has value and if I use it right away I don't lose anything (except marginally faster wear on the battery pack)
The disk issue is about essential function. If I left no spare room the disk would have unrecoverable failures in days or weeks.
The battery issue is only about perception. If I left no spare battery charge the battery would function exactly the same. It's life would only be reduced in that I'd be using it more (this is assuming that my above theory is correct)
(I've been working at a low level with disks for over a decade, writing data recovery apps and such)
I have found in practice that by the time a HDD develops a single bad block, 99% of the time it's on a death spiral and it's going to completely die within a month or two.
It seems like none of this bad block remapping, spare space, or anything of the sort has any effect whatsoever. The only thing that keeps them alive is being well enough engineered not to break at all.
Please correct me if my experienced misinformed me and I'm wrong.
My understanding was the traditional "bad block" behavior was actually hidden - there are bad blocks that occur but the firmware silently remaps everything.
When you see a bad block at the level you can see via e.g. smartctl program, that means the space set aside for bad block remapping is full - the drive has already been silently failing for a while now.