According to specifications, the best Android dual-sim announced is the ViewSonic V350. The GSmart G1310 should be launched in June, some stores have it for preorder already for a couple of weeks. The ViewSonic should be available by end of June / beginning of July.
According to battery life, of course it is shorter on dual sim phones. But it is not a half. There are other parts of the phone shich consume power too (CPU, GPS, BT etc.) I have a GSmart S1205 (a WM dual sim) which lasts about 3-4 days. I would expect these dual sim Android phones to last about 2-3 days. Of course by playing games or surfing the web the battery will be empty within a few hours.