Powering a 14.4V motor - RS550
No, 85A is the stall-current, ie the current it draws if the motor is prevented from moving if the drill gets stuck or so. During normal load you might expect 10 or maybe 15 amps, but use a fuse if you're uncertain.

I suggest you try an old PC-power supply, many of them can supply about 15-20 amps on their 12V rails (pentium 4 and onwards). 12V will probably be sufficient for you app and they are readily availible and often free.

Good luck!