Arduino wants 5 volts (plus/minus 10%) on the 5 volt line, or something over 7 volts on DC voltage input connector. The AA's may be too much for the 5v pin and too little for the DC input. Rechargable Nickel battersy havea nominal voltage of 1.2 volts so four of them that my be ok but be careful because the voltage just after charging may be slightly too much for direct connection.