Official Roland rechargeable battery pack for select amplifier models including CUBE Street EX, AC-33. KC-220 and BA-330. Easy to install and remove. Longer runtime than using AA batteries. Allows the amplifier to deliver more output power and SPL than what’s possible with standard batteries. Premium design with safe, efficient, and reliable NiMH (nickel-metal hydride) battery. ** You can charge the battery whenever you feel it’s necessary. We recommend that you charge the battery at least once a week. ** In the event that you leave the amp on after use and the battery keeps discharging, the battery may over-discharge, causing the safety protection circuit to activate. The battery cannot recharge in this case. Turn on the amp while not in use, and remove the BTY-NIMH/A from the amp.