OK this is going to sound like an oxymoron but is there or are there any ticks to save batt life while using a gps application. let me give an example and what i've tried and maybe someone has a better answer than i do. when i'm out mountain biking i like to have my phone with me just in case and also enjoy tracks of the ride with the gps. so i turn off gps, wifi, all the other usual suspects and launch the gps app. get it going then i dim the screen as much as possible and i'm on my way. However the gps is a hog on the battery life. I keep the phone in an otterbox defender so adding a battery isn't really an option. does anyone have any suggestions on battery life extension or tricks or maybe an actual app that will do tracking and kill pretty much everything else?

thanks