I've got no worries about power meters I just want to be able to plan routes and have a garmin direct me from point a to b without too many wobbles, and being able to find satellites without taking over a minute...
Did you see that Wahoo RFLKT that Dammit posted? It talks to your phone, so all you need is a smartphone and a battery for the headunit. That'd give you up to maybe 9hrs depending on phone, phone use, etc. You could get an external battery for the phone in your jersey pocket too if going longer.
I've got no worries about power meters I just want to be able to plan routes and have a garmin direct me from point a to b without too many wobbles, and being able to find satellites without taking over a minute...