2007 / 2008 Hybrid Battery Question?

Good evening,

I am new here, though I have read messages from time to time when looking for answers to queries but this one I wanted to get a direct answer too, if possible.

I have a 2007 Gen 2 Prius that I had to get a new hybrid battery installed last July. Unfortunately, other issues arose and I had to go and buy a 2008 Gen 2. The new car is in a lot better shape body wise and most everything is in much greater condition, however, the fuel mileage is horrible ATM (partially cold weather related, I'm sure) but I am wondering if the hybrid battery may need replacement.
So, the main question is: Are the 2007/2008 Hybrid batteries compatible? Could be? And how Would I go about making sure. I plan to use the 2007 as a parts bin to fix a few of the smaller issues my new car has, and the battery if swappable, might do good in extending the life of my newer purchase.

Thanks for any and all advice,
CWB

EDIT: I wasn't sure about which model I have.. the list of choices was even more than I knew Prius had for the year.. where would I go about finding out what both my cars are, to narrow down the answer to my question?