can 2 male bettas live in a 3 gallon tank with a divider?
The answer is no. 3g is just about enough for one Betta. We advise 5g to 10g for a betta, but a 3g being an absolute minimum. Betta fish have quite big personalities, in order to thrive, be happy and healthy - they need space to swimming, they also like exploring the tank. A filter and heater is also required. A tank to house two Betta with a divider would need to be minimum 8-10g tank.
Please take few moments to look at my recent blog: http://www.myaquariumclub.com/10-things-to-remember-in- aquarium-hobby-1466.html
Hope it helps and any more questions - just ask!