The JBL Battery 400 is a rechargeable lithium-ion power cell designed to keep your music going in the JBL PartyBox Stage 320 and JBL Xtreme 4 speakers. With a capacity of 9444mAh and 68Wh of energy at 7.2V, this black rectangular battery provides up to 18 hours of playtime on a single charge. To make handling simple, the unit features a red fabric pull-tab that allows you to slide it out of the speaker easily. Since these devices can support multiple power sources, carrying a spare allows you to extend your total listening time to 36 hours, making it a practical choice for long outdoor gatherings or trips where power outlets are unavailable.