Batteries Plus sells a single 1300mAh battery that works in both the Treo Pro and the Blackberry Bold.

If they are interchangeable, then shouldn't we be able to use other Blackberry Bold batteries in the Treo Pro?

Looking on eBay, there are many Blackberry batteries, OEM and aftermarket that are much cheaper, like $3.

Keep in mind that OEM for Treo Pro is 1500mAh, while the Blackberry Bold OEM is 1400mAh, and some aftermarket are less, like the Batteries Plus battery listed above.

(If you are researching, it appears that all the model numbers associated with the Blackberry Bold have the same batteries.)