This is definitely a general rule of thumb for these types of batteries. Higher rate for performance and lower for flight time and life span. In racing we charge at 10 amps even 20 sometimes for performance, but that's not what we are looking for here. Most sources that I have come across suggest no more than 3-4 amps.those who think of using third party chargers with h520e oem batteries 6.2 amp and 5 amp charge rates will work okay but at 4 amps the batteries cells seem to respond better. longer charge time will be conducting flight runs afterwards and compare flight times.