I try to charge my DJI Mavic battery but the first led keeps blinking and i does not seem to charge. The other batterys charge just fine. Can someone tell me what the problem is?

Is it led on the top (by button) or bottom?

Are you charging thru the hub or direclty. Did you try both method with the same result? Plug the battery back in the AC. Turn on the CT/AC/BAT and then check the batery thru the app and see if all the cells have the same reading.

This is going to sound dumb, but I thought I had a bad battery which 'wouldn't charge' and blinked crazy fast when it was plugged in... I found that the battery was actually turned on... make sure the thing is off.  

If you've used the battery and it's not cooled down enough LED #4 (closest to the power button) will blink 3 times per second. Is that what's happening?