The faster a battery is charged the fewer charge cycles it is likely to accept. Best bet is to get a second battery if you really need more range or perhaps consider using your legs to pedal so the motor is drawing less from the battery. Every e-bike I have looked at had a range variance of 100%, or 50 miles little pedaling but 100 miles if the rider's legs did most of the work.
Lithium battery chargers will usually provide maximum charge rates until the battery has a SOC of around 50% and then taper off. I don't know if the brick type transformers are that sophisticated and this is probably why they tend to be low output 2 amp ones. You will also shorten the useful life of a lithium battery if you draw it down to 50% or higher SOC and then recharge it. Batteries are rated for a given number of charge cycles and not amount of recharge per cycle. A battery that is recharged when it is at 20% SOC is likely to last longer than one recharged when it is at 60% SOC as the latter will be recharged more times per mile traveled.