Most of the better high tech battery makers do include a built in battery management system and a small 2 or 3 Amp battery charger, with an optional higher rate charger available at extra cost.
To change to higher tech batteries you will need to make sure they have a battery management system built in or buy a separate battery management system and you will need an appropriate battery charger. They last approximately 4-6 times longer than SLAs, weigh about 1/3 of what equivalent SLAs weigh, and are about 1/3 the size of equivalent SLAs. I went with the more expensive LiFeP04 batteries from Ping. Get in touch with Curry to see if you can increase the voltage to their motors safely.
Adding another 12 Volt battery in series to increase your voltage from 24 to 36 will be heavier and greatly improve your power and speed, but may quickly burn up the motor or at least shorten it's life drastically. Adding higher Amp batteries will increase your range, add to your weight, but not otherwise increase performance and with no danger of harming your motor. The e-bikekit direct drive hub motors I am using are designed to take voltages from 36 to 72, but I'm not sure about the Currie Ezip motor. With battery power, Volts equal speed and power, Amps(or Amp hours) equal range(distance) you can travel on a charge.