Yes they have batteries, but you would need one to store the energy produced from the motor/generator. Either with a built-in battery, at which point its just an electric longboard, or by connecting it directly to your phone or something?

Or perhaps the idea could be scaled down and take inspiration from Dutch bikes by using a small dynamo to power a headlight and taillight or something like that not normally found on a basic longboard without the need for the added batteries or weight.