On their website:
http://thunderpowerrc.com/G6AdvanceE...oBatteries.htm
It states to charge at up to 2C unless you use an approved charger but does not state which it is.
I would never charge at over 2C anyway no matter what they say.
Edit:
Their charger says in the manual that it will charge at up to 30A:
http://thunderpowerrc.com/html/docum...utputchart.pdf