I had a student whose controller power button started blinking red. It will not charge, link to the brain, or connect in VEX IQ software. We have tried multiple cables, we have swapped out fully charged batteries, and I have tried to connect to multiple devices, including a desktop, a chromebook, and my own laptop. No luck on any front.
I contacted VEX directly. and they wanted to replace the battery. I tried that on my own with a different controller battery, and it did not work. After leaving the controller alone for a few weeks, the problem went away, which I know is not a great answer.