Spotify's desktop app is P2P, but their mobile app is server-client. Perhaps advanced users could mitigate the battery life issue in the short run by setting up

Spotify's desktop app is P2P, but their mobile app is server-client. Perhaps advanced users could mitigate the battery life issue in the short run by setting up a "proxy" on a server that joins I2P, while presenting the front-end on a mobile device -- like you would with, say, an IRC bouncer.