Dewalt 12V rotary tool won't charge - any ideas?

Hey everyone, my Dewalt 12V rotary tool (DWA490) suddenly stopped charging. I plug it in, the charger light stays green like it's full, but when I try to use it, it's dead after 2 seconds. Battery is about a year old, not abused. Any thoughts?

Classic symptom of a bad cell or battery management board. If it's under warranty, I'd RMA it. Otherwise, you could try a deep cycle reset: run it flat, then charge for 48 hours. That's brought a few of my Makita packs back from the dead.

Before you buy a new battery, check the charger contacts. I had a similar issue and it was just dirty pins. Used a pencil eraser on them and it worked. Also, you can get aftermarket batteries on Amazon for like $20, they work fine for hobby use.

If you use it daily like me, get a genuine Dewalt replacement. Third-party batteries don't last on jobsites. But try this: press the battery test button. If it shows 1 bar, it's probably a cell gone bad. Dewalt's warranty is decent, call them.

I've got a collection of those 12V packs. One trick: open the case and check for swelling. If any cell looks puffy, replace the pack. Also, sometimes the thermal fuse trips. You can bypass it for a test, but don't run it unattended.