The PlayMakar(R) Pro Expandable Wireless Pods system gives you the ability to expand your therapy beyond 4 channels or pods. Since the system is modular, you can easily replace the channel pods or add multiple pods with the same channel to expand your therapy to an infinite number of pods. It's always good to have backup pods to replace used pods or stash extras at or desk or in your gym bag, wherever you use your unit the most. Features & Benefits Charge pods with USB charger 2.35" pods are extremely portable Wireless pods are easily concealable Backup pods are convenient while other pods are charging