The primary difference between the RS5 and the RS5+ is the type of battery found in each. The RS5+ has a 52V 28Ah LG Lithium ion quick-release removable battery. The RS5 has a 52V 23.2Ah Lithium ion quick-release removable battery. Due to the battery difference, the RS5+ is going to have a 50 mile range*, while the RS5 has a 40 mile range*. LG Batteries are also typically known to last longer as well as have a higher cell quality.
*Ranges and speeds vary on the riding style and weight of the rider.