@Dajark , the IZip Ultra is a beautiful stealthy looking ebike with that internal battery. It has a very early version of the TMM torque sensor in the rear, so you need to be heavy footed on the pedals to really get much from the 500watt motor. Consider that this bike hasn't been manufactured for several years, so that battery is not new and would be expensive to replace when the time comes. One of the companies that rebuild lithium batteries, RPE and Electric Rider and others, may be able to help with a replacement but keep in mind that is an expense that you will be facing sooner rather than later.
Have you test ridden the bike to see how it responds for you? Several of my customers have the bike and most really like the performance. One couple had us swap the narrow tires for much wider, hybrid tires to do some light trail riding while they were traveling. Made for a more cushy ride. This bike can handle your weight but personally, I think one of the Zumas would perform better for you.
As for the 36V to 48V issue, answer is most likely but check that the motor and controller can handle the extra voltage. Over volting can put more strain, heat and wear on all of the electronics and motor which may wear out the bike sooner. If it's an older bike, this could be a creative way to get more power; however, there's always a price!
