series to parallel switch

[hipergp]

This is my first post, Ive been lurking on and off for a couple years and still haven't built an ebike, but have done a lot of reading and playing with the simulator. What I'm wondering is if it would be worthwile and/or feasible to have say, 2 36v battery packs, and a switch or switches to change the configuration from series- 72v and 1x the ah of 1 pack, to parallel- 36v and 2x the ah of 1 pack. My thinking on this is for starting out and hill climbing, or carrying a load, because the top speed of the motor will be different at the different voltage levels. Am I wrong thinking that this would be an electric transmission with 2 "gears"?
Could something similar be done using a transformer to go from one voltage to another? or a "shifter" that takes you through multiple transformers, like gears? or would the amount of copper and magnets required for the watts be ridiculously heavy?

 

[major]

Transformers don't work on DC. And if your system is set up for the high voltage, the motor controller is fully capable to reduce the voltage from the battery to the motor. The controller functions as the transformer and series-parallel switch. There is no need for the extra equipment.