Energy break even date?

I don't know the answer to that, but I kind of have to wonder if it's not a bum question to begin with.

What you really want, I'd think, is more like comparing the energy difference in the manufacture of a pure ICE engine to that of a hybrid engine. Though you also should probably compare the transmissions as well.

While yes, manufacture of the hybrid's HV battery is notable, you're neglecting a lot of the simplifications that the hybrid's ICE has from a standard ICE, as well. And then there's the nice simple transmission compared to most automatic transmissions.

But if you even want to get even more pedantic, there's also how much the Prius saves on the manufacture of wearable brake parts as the hybrid drive provides most of your braking force and not the actual brakes.

So maybe someone out there can give you a meaningless number for how many gallons of gas it takes to produce the HV battery.

But I bet it took even more gallons just to ship the car from the factory to the dealership. (And let's not even get into individual parts shipping to the factory, shall we?) Pointles numbers are pointless numbers, and any number taken out of context is pointless in my opinion.