This is a product to be fitted to a ukulele you have purchased.

It has an LR Baggs undersaddle pickup, which is linked to an active Mi-Si Acoustic Trio Ukulele pre-amp. This boosts the signal to amp or PA, but does so without a traditional battery. It comes with an adaptor which you plug into the mains, and insert a the connected jack socket into your instrument. A couple of minutes on charge and it'll give you 12 hours of play or more.

The sound is super-clear, unadulterated and shows your instrument off really well. I use it myself with Warehouse of Thieves and LOVE it.