I need a <100gram 4S pack (around 850mah) for some smaller builds. 
I'm thinking Infinity Graphene 850mah but not sure about the performance. Can you recommend them?

I used these lipos, Good price and works well. I use those 850 Graphene's in my 3" builds. Tons of power, get like 4min flight times and no sag!

I've been using these on my 3 and 4" builds and really recommend them, they seem on directly on par with tattu 850 4s I think they are exactly the same weight too..