The 12v battery has a fully-charged open circuit voltage somewhere around 13.2v, which is safely within the nameplate rating on the drill. However, unlike Ni-Cd, the voltage droops quite a bit based on the load. With a fully-charged battery and the drill running unloaded and flat-out (no PWM, trigger fully depressed), the voltage droops to 12.3v.
Hot glue was used to cement the battery contact assembly in place.
An in-line 20A fuse keeps things from melting should I touch the wrong things together. :-)