Does anyone have this external battery? I cannot justify >$25 for an external battery and this look okay at $10. I just need something to help the battery last for a few more hours. My use through the average day: Sporadic email checking load two web pages a day WiFi tether to my Mac and/or iPad for 1-2 hours iPod listening for 45 minutes. After this I am lucky to have 5% left. Does anyone know how this battery will help?