The cables on your garage door handle a lot of hard work and tension. Over the years they can fray and degrade. You should change them yearly to avoid the horrible accidents that can occur from these high pressure cables snapping or coming loose.
The battery backup system is a separate device connected to the electric garage door opener. It's useful for power outage and emergencies. It's an easy way to get in or out of the garage since the system is activated as soon as the power's out, the safety features are still in operation, and will last for several hours.