Hi,
There are two prius 1 model:
-the nhw10 (First Japan model)
-and nhw11 (Only model that we can find in Europe)
The nhw10 have round cells (240xD cells)
The nhw11 have rectangular ones.(Not sure but I think 38 x 6.5Ah nimh)
Here a guy is replacing a nhw10 battery with lithium.