Increasing the voltage of a battery.

DC motors should care less about voltage than amperage anyway, car batteries can turn over a car engine, and they're only 12V, but have 100+Ah capacity. If you need more power, just find bigger low voltage cells.

I'm butting in without much knowledge on the subject, but isn't the power generated actually Voltage*Amperage? A transformer simply exchanges one for the other while keeping the same power. We tend to use lower amperage & high voltage because it's less dangerous if someone comes in contact with it.