It used to be recommended that batteries not be charged above 1c because that is all they would handle. now they are making batteries with a much higher "c" rating and the improved technology is allowing them to be charged at a higher rate. in the case of some batteries, up to 10c or higher. i have had no issues yet charging my batteries at 3c (15 amps) as they state they can be charged at 5c, and 8c respectively.