According to the Tria Company, you can use the device for treating your full body without the need for extra flashes. They claimed that Tria 4x can last for up 600 laser hair removal sessions. The device produces 90k flashes. It is enough for 60 sessions. However, most people don’t use Tria for the full body as it consumes a lot of time. It is better for small areas.
Note: you should charge the device once every month if you are not going to use it to extend the battery life.