I have that yak but it has only been up a couple of times. I think you could hit 6 and a half with the stock pack.

I have some gens ace 3300 4s packs that I use in a Handy King and an Advance that I think will also work in this.

A bunch of the guys where I fly are using a little voltage monitor that plugs in to the balance lead and sounds an alarm when vtage drops below what you set it at. Need to get me one of those.

PS the Handy King will fly for quite a while on 3300's.