We really need to standardized battery sizes again...
I bought a flashlight the other day that came with a lithium ion rechargeable the size of 2 AA stuck together. If it ever dies or won't hold a charge, I can just use two normal AA batteries.
It's a really simple compromise to have a "state of the art" battery, yet not be tied to a weird size I won't be able to find. In 30 years I should still be able to buy rechargeable AA batteries.

