I have been using my iphone everyday for multiple things. Decided to get a battery pack to extend the battery time. I chose the Tekkeon MP1280. It basically is a battery that gets used first and then the iphone battery gets used. My question is should these battery packs just be turned on when doinig a lot of web surfing or video watching with the phone or keep it on all the time until it runs out then let the iphone battery take over. This back doubles the time of the iphone battery. It adds minimal size to the phone and can synch phone without taking out of case.