Does it make sense and doable to stack the battery and double the range?

Already asked.
Add an additional 8Kw battery to double the range | PriusChat

You likely won't able to get a pack for so cheap; $10,000 seems more likely.

 

of course it does, but most people don't have the talent to pull it off.

 

I would think the only feasible way to pull something like this off would be to independently charge/discharge the traction batteries which would require a great deal of relay work. A reboot would be needed to switch from one battery to another which would require you to be parked when switching.
Then there is the mechanical work to properly secure such a large mass in case of an accident.
The added weight would require suspension modifications if you still planned on carrying cargo/ passengers.
In the end trading the Prime in for a Honda Clarity or Chevrolet Volt would probable make more sense for someone that really wanted to double their Prime EV range.

 

another prime pack for less than 3k is worth it no matter what.

 

At first glance, this seems like a challenging thing to do, the pack isn't _that_ lightweight, and adding capacity that way would be challenging to do but not impossible. Adding this safely would be a whole nother story. Aside from the weight, the power levels are not something to trifle with.

People have paralleled traction packs before however. Early ~2007 or so (?) plug in priuses were all sorts of weird, but a lot was learned about what would, or would not throw a DTC. At least a few of them did play with paralleling packs.

Dynamically switching in two packs at different SOCs would be an architectural change for the prius, nontrivial to implement as well.

Parallelling the cells on the other hand would be much easier to do. It would likely require a custom BMS, and other engineering work, but IMHO _much_ more approachable even for the dedicated shadtree. Not that it would be a safe (or sane) thing to do.

 

looks difficult at second glance as well.

 

Trade it in on a Volt or Clarity and more than double your range; comes with a warranty and everything!

Messing around with a Prime in a manner such as this while it's still in warranty is fool hearty.