One of the biggest problems with Ares Amoeba AM-013, AM-014 and AM-015 is the limited battery space. You should use small size batteries. The Airtech Solutions Battery Extension Unit is specially designed to provide twice the space and requires no modification for installation. Made of fiber reinforced plastic strong, flexible and resistant to impact from bb's. More space for a larger Lipo means less frequent Lipo changes and therefore longer playing times. With the extension unit, Lipo's up to approximately 135 mm x 40 mm x 18 mm can be used. Available in Black & Tan color.