3600 is a big pack.

Batteries 101:

mah stands for milliamp hour. 1000mA = 1A, so for example, 3600mah = 3.6ah. This means that if you put a 3.6 amp draw on the battery, it would take 1 hour to fully discharge.

Thinking in reverse, if you charged it at 3.6amps and it was dead, it would take 1 hour to charge. The lower you charge at, the longer it will take. Charging at a lower setting will help against peak detection problems, which help to get a better charge on the battery.

I charge my 3300packs in my starter box at 2amps and have never had a problem. When they are real low, it takes forever to charge, but that's ok. I start the charge before I go to bed and when it's done it'll simply trickle charge. In the morning, I swap to the other battery, start it up and head off to work. When I come back, they are ready to go .

Charging at high amps, like 4 should only be done in an emergency. Say you forgot to charge your batteries and you need some charge just to get you buy, then go for it. Otherwise stick to the lower settings for longer battery life.