Most phone batteries
are electrically compatible, just not physically compatible. I have used Droid phone batteries to power HTC phones by holding the battery in place against the contacts, even though it didn't fit into the phone at all.
On the engineering side, we should push for standards, and for components which operate the same at higher and lower volatges (2.0v, 2.2v, 3.0v, 3.5v, 5.0v, etc) where possible.
