Are you sure that the cordless power tool companies actually want
that? If they did, I would expect all the batteries to have the same
charger and at least have the same package and connector. That's
hardly the case. No sooner than a new model appears, I find myself
buying yet another charger and new batteries.
My guess(tm) is the "good" battery packs have internal chargers
because that's the only sane way to provide balance charging for
series connected LiIon cells. The balance circuitry could have been
in the charger, but then there would be at least one wire per cell
going between the battery and the charger. There would also need to
be wires for temperature sensing. The rest of the circuitry inside
the battery pack is the BMS (battery management system), something for
the "fuel gauge" indicator, and counterfeit tool/battery detection.
You might want to look at some YouTube videos of various battery
powered power tool and battery pack teardowns.
<
https://www.youtube.com/results?search_query=boltr+battery>
I think you'll find this video interesting or at least amusing:
<
https://www.youtube.com/watch?v=8b9ZYt6MzHc> (14:49)
In the beginning, he discusses DeWalt 20/60v battery pack
compatibility vs LiIon shipping regulations. Near the end, he kills
two cells in the pack by cutting the pack apart with a reciprocating
saw.
I have a few DeWalt LiIon power tools. The battery packs have very
little electronics inside:
<
https://syonyk.blogspot.com/2016/09/dewalt-20v-max-30ah-battery-pack.html>
It has the standard BMS board, but no balance charger circuitry. I
guess(tm) you would consider this battery not so "good".