Protects Your Battery From The Rain, Snow and Keeps the Battery Insulated - Insulates battery to help operate more efficiently - Protection against the elements while riding or transporting on a car rack - Scratch protection - Pocket for phone (keys or wallet) - 4mm neoprene black - Medium: Fits diameters 3.5" to 4.5" in diameter - Large: Fits surface-mounted battery and is compatible with Bosch, Shimano Steps, Samsun, Yamaha.