Well, I would try other batteries (from a different and trusted brand) first. Even though the voltages seems fine, they might not be. For one thing, the batteries must not only have a certain voltage level, but they also must be able to sustain it. When you connect a attery, they wil allways output a higher voltage at first, then it drops. When you disconnect it, then reconnect it, you'll see the same thing. It's due to the chemics (you gave the reactions some extra time while you had them disconnected, to put it simply).