Most, and i repeat, MOST, brushless kit controllers can be run on higher voltage without any modifications.. as long as you dont care about the LVC setting ( low voltage cutoff )
crystalyte, infineon, 9C, E-bikekit, A2B, Wilderness Energy, i have personally all run those stock 36v at 48v without any problems..
You do want to consider that if you have one of those LED throttles, set for 24v, may not like higher voltages, but if it's a non-led throttle it makes no difference ( the led wire can simply be cut from the throttle connector to disable it )
some of the better controllers do have USB type connectors that you can use to program thorttle response, LVC, etc etc etc but no need for that on 500w setups.
Sources for good pre-built lithium packs, ebikes.ca is one i can highly recommend, ping is the duct tape from china ( actually now comes with normal heat shrink vs duct tape lol ) lower end but trusted vendor, there are many more but paying bottom end prices usually gets you what you paid for..
Me, personally, i'm using turnigy and zippy lipo packs from hobbyking.com but that requires an informed and risk taking individual..
i've spent 1000's ( more like 10's actually ) searching for the holy grail of battery tech and i canot say that it's available yet, there are diy solutions and some better pre-built packs but nothing is perfected yet... it's early days..
