18650 battery pack 4S 14.8V 2500mAh is rechargeable and safe.
Amazon.com: HOOVO 4S Lipo Battery 9200mAh 14.8V 100C with XT90 Plug Metal Plates Soft Case for RC Truck Truggy Buggy Tank RC Car Racing Hobby (2 Pack) : Toys & Games
CNHL Black Series 2200mAh 14.8V 4S 30C Lipo Battery with XT60 for RC Airplanes, Helicopters — ChinaHobbyLine