The yellow Brunton Revolt 4000 Portable Power Pack is a durable source of power while you are out adventuring. It features a water-proof and sink-proof construction with a shock absorbing polyurethane outer shell. This waterproofing is completed by using an Aqualoq door over the USB port to keep water and dirt away from the electronics. The Revolt also has a large capacity of 4400mAh, allowing for approximately 3 smart phone battery charges