On flat ground, the weight of the larger batteries will affect acceleration, however, will not affect top speed very much. When going up inclines the extra weight will affect the top speed more significantly.
For better top speed and acceleration performance, there is not much that can be done without major modifications such as custom installing a larger motor and controller. Some people overvolt their EcoSmart scooters to 48 Volts and get better performance from that modification, however, overvolting the motor and controller can lead to overheating and burning out these parts so it is something that we recommend doing with caution and warning.
For 15Ah batteries, a 1.5 Amp charger is the lowest power one that should be used and 4.5 Amp is the highest power one that should be used. Using a battery charger higher than 1.5 Amps will not damage the batteries but instead, it will slightly decrease the lifespan of the batteries compared to using a 1.5 Amp charge, so it is nothing to worry about.
We carry speed controllers for the Razor EcoSmart scooter on our EcoSmart Parts page and also on the 36 Volt Chargers page which can be shipped with overnight shipping for the fastest possible delivery time. Any of the chargers on the 36 Volt chargers page over 1.5 Amps and which have a 3-Pin XLR plug are compatible with the Razor EcoSmart scooter.