RE: what amps to charge at
The standard recommended charge rate is 1C, which is calculated by taking the mah of the pack and dividing by 1000 to get a amp number for charging.
3300mah / 1000 = 3.3amps - that would be the standard recommendation.
I like to play it safe, and take extra special care of the packs, so I run 85% of the standard recommended charge rate
3.3amps x 0.85 = 2.8amps