I'd mostly worry about mass ratio, though they do drop off some of the batteries half way on the second stage.
Batteries are heavy, but the system can make up for it. More precise control of propellant volume means the combustion chamber and nozzle don't have to be engineered for such high peak stresses due to a turbopump surging.
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.