To be able to run my Pi at any location I built a battery powered power supply for it.
Its base is a 8x battery holder (8x 1.2V-1.5V = 9.6V-12V) so it is guaranteed to provide stable 5V+.
To get down to the 5V needed by the Pi I am using a switching BEC (SBEC) which is a very efficient power regulator. The one I used can be found here.
For a maximum of flexibility I decided to use a USB Type A plug so that this power supply could supply any USB based device with power. I even can use it to charge my mobile phone.
As shown the Pi is connected using a ultra short USB Type A -> Mini USB cable.
The power plug is assembled with standard Eneloop rechargeables of the 3th generation
so the powery supply delivers 8x 2000 mAh = 16.000 mAh.
This power supply delivers nearly 4000 mAh (see comments below)
My first test for the battery lifetime was disappointed:
I did connect to the Pi using ssh and printed out the uptime in a while loop with a sleep of one second.
The Pi did stop running after 7h 49m.