I've got a few 700 and over size helis. My advice would be to avoid using Rx specific packs. I personally prefer to use a standard 2S LiPo with something like 25-30C rating and about 2200mAh. With one of those you can easily get six flights with capacity to spare (no need to have two onboard). The reason I avoid Rx specific LiPos is that they tend to have low 'C' rating and so suffer from bad voltage drop under load. Probably some of them are fine but i know of some that have really bad voltage drop, standard LiPos tend to be cheaper anyway.
Your Microbeast 'HD' makes wiring a battery to the FBL much simpler, you dont need to worry about splitting the supply into two servo plugs.
FWIW this is what I've used on a few helis:
ZIPPY Compact 2200mAh 2S 25C Lipo Pack (US Warehouse)
The other option of course is a good quality HV BEC powered off the main flight packs but that is a more expensive way to do it and batteries are probably more reliable.