View this product description in Norwegian.

Don't let your recording session stop in between Hirose battery pack swaps or away from AC power. The BCF-8 battery case has been custom-designed for the ZOOM F4 and F8 MultiTrack Field Recorders, as well as the filmmakers and sound designers that use it. Load up some BCF-8's with eight AA's a piece (four on each side) for peace of mind. Use the F4 and F8’s advanced power switching feature to it’s full potential by automatically switching between Hirose and AA battery power without interupting your recording. 

The lightweight, plastic BCF-8 is a perfect, convenient backup power companion for your F4 or F8 recorder.
Redundancy is always good...always.