While the 2B can run on a 9V battery, using the official E-Stim Systems Power Supply provides roughly 30% more power and prevents the rapid battery drain common during long audio sessions.
In the community, "top" refers to three things: Popularity (download count), Effectiveness (feel/orgasm quality), and Safety (no DC offset or voltage spikes). The absolute best files share these traits: estim 2b audio files top