Great question! Any of our SoundTouch products will be able to sync up with the Wave SoundTouch IV via the SoundTouch application, and play any audio that is either a source within the SoundTouch application, or via Bluetooth to all SoundTouch speakers.
Currently at the moment, we do not have any SoundTouch systems that would feature a lithium-ion battery. Having said that I would certainly recommend the SoundTouch 10 or 20. The SoundTouch 10 is small enough where it is very easily moved from room to room, but also packs a very powerful punch when it comes to audio.
You can find a list of our SoundTouch compatible devices using the link below (excluding the Lifestyle 600 and Lifestyle 650):