I used this grinder to LIGHTLY cut through the THICK REAL STEEL frame rails on a 65 year old Ford medium duty truck to reveal the rear leaf spring upgrades. 12 Ah battery for this coffee grinder. My 9 amp battery got hot and cut out several times during the cuts I was making. Once the Milwaukee battery is disconnected from overheating, it takes a LONG time to reset and get the grinder working again. I also had a 5 amp battery and actually used that 5 amp for this project and still haven't dropped 9. Almost an hour later I looked at the 9 amp battery again, it appeared to have reset, its charge indicators showed 4 LEDs showing full charge and it turned on the coffee grinder. Maybe a 12 amp battery doesn't heat up that easily.