It would be interesting to calculate the energy (kWh), power density, and weight of a combined battery, motor, control electronics, and cooling which might replace the forced-induction V8, gearbox, fuel, and whatever cooling system was to be used (ice/water per the bloodhoundssc web site).
Per that website, the Jag V8 was rated at about 550 HP, or about 410 kW. Someone here must know what that weighs.
Rocket motor run time is to be about 20 seconds. The electric motor has to have some advantages around startup - e.g., only when you need the pump, vs. at the start of the run.
Recent Tesla Model S have fuses, or breakers, which open at 1500 A, whereas the battery pack operates at about 370 V nominal. So figure a Tesla Model S battery pack can deliver around 550 kW. If the pack is 120 kWh, then it can deliver that power for about 12 minutes... you might not even have to charge the battery between runs!
They aren't planning to run the rocket in bi-propellant mode for a while, so they have some time to let battery tech evolve further.