Yes this will indeed work as I have modified my electric lawn mower. I have used the lithium batteries used for RC flight at hobbyking and just link them in parallel or series to get proper Voltage or Amps you need. The lithium polymer battery packs are light but only last about 2 years and the power will start to degrade. I have had more success with the 18650 cell packs that are used in ebike batteries and corless tools. Lunacycle is a great place to get these packs or you can find similar on Aliexpress for cheaper but not guaranteed the same quality. The key thing is to use a connect that can handle the wattage draw from your motor. I recommend the XT-60 or XT-90 connectors Good luck with your conversion.
Cheers!
ian