Garmin 296 is a better bet for helis than the later models. Battery life up to 8 hrs if you use the screen backlight sensibly. Easily programmable via USB. And (for the UK) the street map software add-on is excellent. So you have a device which you can use on the road or use to find exact streets from the air.
RAM do a great suction mount and Robin Aviation in the USA supply a nifty R44 mount for the back of the cyclic.