I was surprised to hear they were using LION packs, dropped mid second-stage. I'm not sure why but I expected super-capacitors or maybe flywheels arranged gyros

I was surprised to hear they were using LION packs, dropped mid second-stage. I'm not sure why but I expected super-capacitors or maybe flywheels arranged gyroscopically within the stages. Batteries are heavy - but must be the best fit for now.