Disclaimer: Lithium batteries are dangerous and can explode/catch fire if used improperly. You are solely responsible for your own safety if you decide to make this adapter. I am not an electrical engineer so I am not going to go in-depth with how to wire it, if you are not familiar enough to wire it on your own, you should not be working with lithium batteries until you are more comfortable with electronics.
All credit for the M12 Battery sockets goes to timskloss on Thingiverse.
This Adapter replaces the standard NIMH battery of older 3M Adflo blower units with sockets for Milwaukee M12 batteries. This Adapter is either secured to the lid of an old battery and connected in the original way or secured to the blower housing with M3 screws. Battery sockets are secured to the adapter with plastic bonding epoxy. Each battery has a low voltage cutoff board wired to it and the two batteries are connected in parallel. A boost converter is used to boost the voltage to the needed 14.4v. I included the circuit board and thermistor from the original battery to this adapter as well as a cutoff switch for the batteries.
Required Hardware:
The author hasn't provided the model origin yet.