There are many standard lithium ion cell sizes, here is a list: https://en.m.wikipedia.org/wiki/List_of_battery_sizes#Lithium-ion_batteries_(rechargeable) https

There are many standard lithium ion cell sizes, here is a list: https://en.m.wikipedia.org/wiki/List_of_battery_sizes#Lithium-ion_batteries_(rechargeable) https://en.m.wikipedia.org/wiki/List_of_battery_sizes#Lithiu... Many battery packs (power tolls, Tesla, and more) are just a bunch of cells ganged together with a battery management controller inside a plastic shell. The problem lies in the connectors/controllers being proprietary.