Dewalt sander battery not charging - any ideas?

Hey everyone, my Dewalt orbital sander's battery won't charge. It's the 20V max. I plug it in, the light flashes red, and it doesn't charge. I've tried a different outlet and the charger seems fine (charges my other batteries). Any ideas? Thanks!

Could be the battery contacts. I had that happen once. Try cleaning the metal contacts on the battery and the charger with a pencil eraser or some rubbing alcohol. That might fix it. If not, maybe the battery's just dead. How old is it?

Red flashing light usually indicates a temperature issue. If the battery is too hot or cold, it won't charge. Let it sit at room temp for a bit. Also, check the voltage with a multimeter if you have one. If it's under 15V, the battery might need to be jumped or replaced. There's a chance the cells are imbalanced.

I've seen this happen if the battery is completely drained and the charger can't detect it. Sometimes you can revive it by putting it on the charger and gently tapping it (not too hard) or using another battery in parallel? Actually no, don't do that. Best to check if it's still under warranty. Otherwise, try the eraser trick and if that doesn't work, it might be time for a new battery.

Thanks for the replies guys. I'll try cleaning the contacts and leaving it for a bit. It's about 2 years old, so might be past warranty. I'll check the voltage too. Appreciate it!