[mitthrowaway2]

When I said lithium-ion I was indeed referring to secondary (rechargeable) batteries. Apologies for not making that clear.

AA and AAA Nickel-metal-hydride rechargeable batteries exist, but it doesn't seem anyone ever made a li-ion equivalent.

[ssl-3]

Lithium rechargeable AA cells do exist, and they're perhaps even more mind-bogglingly complex than you'd ever imagine: https://paleblueearth.com/products/pale-blue-lithium-recharg...

In order for them to function: They've each got charge circuitry, buck converter circuitry (to get down from 5v to ~3.7v lithium voltage for charging, and from ~3.7v lithium voltage down to 1.5v to be compatible with end-user devices), and each one includes its own USB C port.