It's on their website (not actually in their instructions). I had read a review somewhere else, and they stated that they did not know about the charging requirements and destroyed their earphones from overcharging them as a result.
I thought that if this was an issue with their earphones, then they should have supplied a charger or made it explicit in the instructions. I had been charging them with my iPad charger, so not sure how much damage I may have caused.
They also state to avoid charging them in your car, as most cars output 2.1A.
The wording from the Jaybird website "HOW DO I CHARGE MY HEADPHONES?
Analyze the primary power and charging source. We find computers to be a great, safe method. Anything that is less than 1 AMP is safe and recommended. Car chargers produce a much greater power supply, so we recommend staying away from those. Over charging your battery will quickly reduce the life of the headset, so along with monitoring the power supply, try to keep your charge time limited to 2.5 hours and always try to run the battery out until the unit is dead."