Had it used for a multi-day bike trip over the Alps to the useful life of my smartphone (Samsung Galaxy S4) what my navigation aid was to extend (only GPS on). I could therefore use the smartphone for more than 5 hours without it fully to discharge (instead of only ~ 2 hours). If you switch off the screen in the meantime, increasing the useful life further. If you still have a second set here at four AA rechargeable batteries / batteries, you can probably min., Offers 8 hours of use.
I have loaded the smartphone at a battery capacity of 50% to the bearing device. The smartphone battery was then loaded despite use to about ~ 70% and ~ 50% went on back down to the four AA batteries (2500 mAh) from the storage unit were empty. The whole thing took about always 3 hours. (Only on GPS; if you switch off the screen in the meantime increased to the length of use).
This part is great for travel in combination with a good AA Ladegrät, such as the BC-700 (). The latter can be good batteries (eg 2500 mAh) Fully charge within 5 hours (without memory effect).
Is also very convenient that the part is so small that it, together with smartphone in my bike mount () fits, where it is thus protected against water.