Along with being both spacious and portable, it's essential to find something that can protect your gear. Check to see if the bag is padded, waterproof, and shock-absorbent. Even if it weighs down your load a touch, finding a battery that can go for days without leaving you powerless can make that extra weight worth carrying. After all, you never know what kind of unexpected pitstops your journey might involve. Best to approach them with a full battery.