Depends on the pack and the charger. Generally you should follow the rates on the label (for most, it would say 1C charge, which would be 1.8A on the 1800mAh pack). Some chargers (like my Hyperion) claim to safely charge at 2C, and I know of people who do it all the time, but YMMV- check the instructions that came with the charger for what the mfr says about that, and whatever you do, don't experiment with it indoors . Regardless of all that, the safest is always going to be 1C.