Correct me if I'm wrong, but the Prius V is all gasoline, meaning it's not got any other energy source than the gas. All the electricity ultimately comes from combustion. I did a plug-in conversion of my 2008 Gen2 years ago and installed a 6.5kWh Lithium-Ion pack in place of the .6kWh (usable) NiMh original. I'm not sure offhand how much usable capacity exists in the V, but it's probably around the same which means you can't really do what you want. Besides, Toyota has spent tens of thousands of engineering man hours to prefect the ratios for the best economy. I suspect if you tilt the balance toward electric it's just going to force the gas engine to run in long spurts to recharge the battery, putting more stress on the battery and actually REDUCING your mileage! If all the power has to come from gas, you are much better off avoiding to conversion losses.
Now if you plan on plugging it in, that's another story, but it's super dangerous and a lot of work for not much capacity. Mine would do about 40 miles city and 20 on the highway in all-electric with extensive mods. The internal capacity of the OEM NiMh pack combined with the larger mass and higher drag of the V, means you're probably lucky to get 2-3 miles of all electric even at only 25mph. And then, how does the battery get recharged?
Even after all the work I did on mine, it was a comparatively poor EV. I now drive a Nissan LEAF and I love it! Sadly, It's a much better solution than what I came up with and it's much more fun to drive. I still have the Prius in the family for occasional trips, but it's lucky to see a few thousand miles a year.