The minimum amount of energy required to pump a given quantity of propellant against a given chamber pressure is fixed, and not low. Doing it in a shorter period of time only makes the *power* requirements *higher*. You also need enough batteries to supply your power demands with the batteries partially discharged, so the effective energy density is reduced.

For a rough, BOTE calculation: they claim a thrust of 4600 lbf and specific impulse (vacuum, presumably) of 327 s. Mass flow rate is something like 6 kg/s. Very roughly approximating the combined LOX and RP-1 density as 1 g/cm^3, assuming a Merlin 1D-like chamber pressure of 9.7 MPa, pumping with 100% efficiency takes 62 kW per engine. Realistically, more like 100-200 kW, or 1-2 MW total.

Also, the rocket's not going at anything close to 30 gravities. All 9 first stage engines at peak thrust could only push about 600 kg at that acceleration.