Hello wells,
Quick note to remind you that handling LiPos is something that you should be very careful with.
As far as my understanding goes, you can charge a LiPo safely at 1C, this means that for the 6600mAh you could charge it at 6.6A and for the 2500mAh at 2.5A. However, it’s better not to assume and follow each battery specifications, If you send me the link to your products I can confirm this. From adafruit I could not find any 6600 nor 2500 Lipo, only Li-ons which have a different charging rate, in the case of Adafruit’s ones they are about 0.5C so you can charge them at 3A and 1A but you do need to find a charger that is able to provide those Amps, Adafruit’s charger can provide up to 1A.
There are special batteries that have a higher charging C rate which allow you to charge them faster. This requires bigger chargers and a proper power source that can provide the current in order to charge them.