I have a LiPo batterery:
EZ-power LiPo 4000mah - 2s 7.4
How could I power the Raspberry, I just know that Pi works at almost 5V.
You want to use a step-down power regulator that will take your 7.4V LIPO battery and take it down to 5V. You could, for example, get one of these: http://www.gearbest.com/development-boards/pp_69337.html?currency=GBP&gclid=CJbgve25_cQCFWH3wgod-acA-w which takes in the + and - from the battery, steps it down and then gives you USB ports to connect your Pi to. Be aware that the regulator may get a bit hot due to the dissipated energy and also be careful not to over-use your LIPO.
I just use UBECs (a couple of GBP on eBay). E.g. http://www.ebay.co.uk/itm/111625837178
They take something in the range 5.5V to 26V and convert it to 5V.
I just connect the UBEC inputs to the battery and the UBEC outputs to the 5V and ground pins on the expansion header.
I have bought for example this: http://www.gmelectronic.com/powerbank-pd004-5200mah-p751-664 . And I did run timelapse snapshots for many hours (10) before I switched off RPi. I suppose any powerbank for phones (5V) is ok.
The battery you refer is dedicated to RC models, I would be worried to connect to RPi.
Edit: You can use a voltage regulator - see e.g. LM317T http://www.reuk.co.uk/Using-The-LM317T-To-Regulate-Voltage.htm or http://www.learningaboutelectronics.com/Articles/LM317-voltage-regulator. It is based on Zener diode, you will waste some energy to heating the regulator.
This is an old thread but just if somebody needs quick way to solve this issue can use phone car charger that are sold for $5 almost everywhere (they have 2.1A version too). It contains switching regulator (DC to DC converter) inside. Also it has USB port/s that can be used to power your Raspberry Pi .