Tiltrotor support for plane

I did my first hover of a FireFlyY6 yesterday
New photo by Andrew Tridgell
I’ve had this plane for a while, kindly sent to me by Andy Trench. We finally got the build finished on a Saturday CanberraUAV build day, and did a first hover on Sunday.
The plane hovered fine, but the battery voltage and current has me stumped. I used the recommended 3S batteries, which are the high-capacity 3S multistars, 5.2Ah, two of them in parallel (one in each wing). In a 90 second hover the battery voltage dropped from 3.9volts/cell down to 2.6volts/cell. We landed it at that point as the voltage was well below the danger level.
The current logging shows a current draw in hover of around 80A, which is a lot more than I expected. Total power draw in hover was around 700W.
We’re clearly going well past the C rating of the battery, which is surprising as this is the recommended battery setup. Has anyone else flown the 3S default setup with the FireFly6? If so, do you have a flight log you could share so I can look at the voltage/current?
Cheers, Tridge