Circular saw battery won't charge – any ideas?

Hey guys, my 20V circular saw battery stopped charging out of nowhere. It's a DeWalt 5Ah, about 2 years old. The charger shows solid red light, no blinking. Tried another battery on the same charger and it works fine. Battery is not hot or swollen. Any thoughts before I toss it?

Had the same happen to my 6Ah. Try cleaning the contacts on the battery and charger with a pencil eraser or rubbing alcohol. Sometimes it's just crud. Also, leave it on the charger for like 10 mins even if it looks dead. My 5Ah came back after an hour once.

Solid red usually means a cell imbalance. If you got a multimeter, check each cell group (B+ to B-). If one is below 1V, it's toast. Otherwise, you might revive it with a gentle charge on a NiCad mode if your charger has that. But honestly, for the price of a new battery, I'd replace it. Harbor Freight has cheap ones that work okay.

Don't bother salvaging it if it's 2 years old. Lithium batteries degrade, and a dead cell can be a fire risk if you try to force charge it. I've seen too many shop fires. Buy a genuine DeWalt replacement or a quality aftermarket like Powerworks. Also, are you storing them in a hot garage? Heat kills 'em fast.

Thanks all! I'll check the cells with my multimeter tonight. If it's a dead cell I'll just buy a new one. And yeah I do keep them in the garage... maybe it's time to bring them inside. Appreciate the help fellas!