The Goal Zero Rechargeable AA Batteries 4-Pack works with the Guide 10 Powerpack (sold separately) to keep your flashlights, headlamps, automatic coffee grinders, and other AA battery-powered gadgets alive and well no matter where you are.
They last a decent amount of time with a full charge, can last a full day in my GPS and quite a while longer in my head lamps. I got 2 sets of the AA and 2 sets of the AAA and it seems to suit me well for all of my battery needs in the back country.
These last a long time; they're not like your old school rechargeables that die in an hour. I use it with the Guide 10 and carry it in my bag just to charge my iPhone if I need it. I haven't tried Eneloops but I've heard that these last about the same times.
The batteries are great. I haven't used them in any other system than the Goal Zero Guide 10, which I take everywhere with me. Extra batteries are a great way to turn the Guide 10 into an extra unit at a low price.
These worked well for me to keep my iPhone going all day (literally) in GPS mode.