Angle grinder stalling under load - battery or motor?

Hey all, my cordless angle grinder (18V) keeps stalling when I put any real pressure on it. It works fine at no load, but as soon as I try to cut metal, it bogs down and stops. I've tried two different batteries, both fully charged. Is it the motor or something else? Anyone else had this?

Could be a few things. First, check the brushes if they're worn - that can cause loss of power. Also, might be the gearbox needing grease, but stalling under load sounds more like a battery or motor issue. Have you tested with a battery known to be good from another tool? Also, what's the amp-hour rating of your batteries? Low AH can cause this.

I've seen this on older grinders where the carbon brushes are shot. Also, if the armature is dirty, it can arc. But first, check the basics: make sure the disc spins freely, the spindle lock isn't partially engaged, and the gearbox isn't full of gunk. If it's under warranty, maybe get it serviced. I had a grinder do that and it was the switch contacts heating up. Replaced the switch and fixed.

I agree with checking brushes. If the grinder is several years old, brushes are a common wear item. Also, take the disc off and run it - if it doesn't stall, then it's the disc (maybe too thick or binding). But if it still stalls, it's likely the motor. Also, check the battery contacts - dirty contacts can cause voltage drops. A bit of electrical contact cleaner might help. Good luck!

Thanks everyone! I'll check the brushes and give the contacts a clean. I didn't think about the switch or the disc. I'll take the disc off and test. If it still stalls, I might take it apart and look. Appreciate the help!