my 36V10AH Limn2o4 battery from conhismotor never had sag! But I only had 2/3 of the advertised capacity
What is happening is my bike is moving like I was stopping the throttle from time to time. That's what is sag for me: mini-stop where the bike doesn't run anymore for half a second then continue working.
Too bad to have sag with 30C lipo. I was thinking about getting the 15C zippy for their price, would that be worse?
Yes, it had sag, absolutely. You have obviously not measured it. That battery puts out a fraction of power that your new RC Lipos can.
All batteries sag to some degree, unless maybe you are applying a 0.5C load on a 90C nanotech.. you probably need a 5 digit multimeter to measure the voltage drop...
Yes, the zippy 15C would have double or triple to triple the voltage drop per equivalent load and amp hours.
When the power suddenly cuts out, that is not sag. sag is when voltage drops, the battery makes heat, and you lose watt hours. It doesn't make your power cut out intermittently.
Are you running a cycle analyst with amp or speed limiting? what kind of motor and controller are you running?
9A seems like an awfully low amp rating...