What is the source for the Androids unlimited energy supply? Do the Androids have ki or another source of energy? If so does, Android 16 have ki since he is fully mechanical and only living beings have ki?
I'd like to believe she has Ki, because she is part human.  At the world tournament Goku asks how her and Krillin had a child together and he explains that she was human to begin with and turned into an android by Dr. Gero.
(Season 7 episode 208 or 209)(I can't remember exactly)

"The correct term is Cyborg. Human with cybernetic parts, she was human by birth and turned into a cyborg, thus retaining certain human functionality, such as being able to get pregnant."

But that still raises the question why Goku and the others couldn't detect their energy. I guess some things should just be left unasked?