Lego Train Bricks Powered UP Hub Bluetooth AAA Battery Pack Receiver 88009 NEW 673419309097 | eBay
Electric 9V Battery Box 4 x 14 x 4 with Red Buttons and Contact Plate with Dark Gray Base (2846 / 2847c00) : Part 2847c01 | BrickLink
Amazon.com: DooQi CADA Technik Power Function Kit for Technical Cars, Including 3 Motors, LEDs, Battery Box and 2.4 Ghz Remote Control (Compatible with Many Models Such As CADA) : Toys & Games
Keybrick One – Keybrick
Batteries and Battery packs
LEGO Power Functions 8881 Battery Box 8883 XL M Motor IR Receiver Controlled Set | eBay