I found the missing 4" (vertical) in the trunk. It is below the battery.

I can't speak for everyone else but I think we get that, there was a discussion about whether it needed some additional airflow over the exterior, although IMHO that now seems less likely. But your details about the blowers are certainly very enlightening and appreciated.

If I understand correctly you are saying that the four inch tall open area is nearly the size of the battery, correct? In your original photo it seems that the battery extends a few inches past the opening, at least in that direction, presumably that is where the battery rests and is attached, and the same thing on the other end of the battery, is that correct?

If so then it's a question of did they create that space specifically for additional cooling, or did the space already exist and they just couldn't design a battery that would fit in it, or did they have some other unknown reason for placing the battery where it is thus leaving wasted space below it.

 

Creepy Factor?

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The round space sure looks like the spare tire space on my Gen 4. They likely used the same chassis for the Prime.

 

So, if I understand the discussion, the "purpose" of having that few-inch gap under the battery is to allow air ventilation, as an alternative to liquid cooling, because air cooling requires less equipment (less weight, so less energy needed to transport the vehicle) and is less expensive, and this was the compromise that Toyota chose to go with.

 

No. That’s just a theory that is more just a rationalization of Toyota not doing anything different in the trunk to repurpose the space used for the Gen 4’s spare.

 

Gen 4 is far lower-slung than a Fit, though, which reduces available space for a fuel tank down there.

 

The space is likely to keep the battery off the pan during a collision any other reason is probably silly
(But still possible)

 

What?

 

Don't forget, a precedent had been established for mid-cycle updates. Room to grow when cost justifies is a good idea.

Also, don't forget about weight & safety. Simply cramming in more battery because room is available doesn't make it a good idea.

 

I don't think most people here want more battery, they want more efficient use of the available space, to get a more useful cargo area.

 

The Prime uses the chassis of the gen4 with no modifications. That space is for a spare tire. Earlier Prime designs may have placed the battery in that depression or not, but if so, that design was axed for having too short of an EV range.

The air cooling takes place within the battery case. Some heat will be given off through the case, but being in direct contact with the metal frame might be more effective for that than air.

Air cooling is cheaper and lighter than liquid, but the packs need to be bulkier to allow adequate airflow with in them, doesn't provide any heating on its own, and the cooling is less effective over all. These are fine trade offs for a PHEV of a range like the Prime's; the Ioniq PHEV and Energis also use air cooling. PHEVs cost more than a BEV because of the ICE and all, so you want to cut costs where you can, and there is the ICE to get you around if the battery ever gets too hot.

The compromise Toyota made all has to do with their choice to not making any modifications to the gen4 chassis and fuel tank and keeping the traction battery in one piece.

This is just another rationalization. A collision of the rear is going to come at the battery from the side, not the bottom. As for debris hitting the under carriage, there is already a sizable gap between the road and that bottom panel to make room for the exhaust and suspension. Considering the energy that any debris would need to pierce that panel would mean such would only happen real the car is moving forward. This would make the gas tank more likely to be hit. The cases of the Tesla's all had the battery damaged in front of the passenger cabin.

 

I don't need more useful cargo area (you probably meant "volume"), but a flat cargo area when the seats are folded would make the existing volume easier to use and more useful. Further, if that space under the battery were somehow accessible, that would be fantastic for what I used my underfloor tub in my 2004 - hiding expensive things like laptops when I'm carrying them.

 

Turns out, what we have from Prime works fine for that.

We've been surprised just how practical it has been, considering the first impression leads you to believe it's really small.

 

Where do you hide them? There's absolutely no place to put my laptop in a Prime that is out of sight.

 

With the cover retracted, both backpacks with laptops fit, along with a long rubbermaid bin for most stuff

 

Oh, the tonneau cover. To me, that thing says, "I'm hiding something expensive, please break in and see what it might be." The thing I liked about the underfloor bin was that the entire back looked completely empty even when it was housing $10k in electronics.

 

Since mine is always covering the cargo area, I never think of it that way.

 

right...to hide the battery and retain space we probably gotta go back to a Gen3 bulbous shape

 

And mine is nearly always in my garage.