Can't SSH into PI

[Ruenzic]

I am able to ssh into the pi from my laptop when the pi is being powered by its usual usb power lead.
But as soon as i unplug that and plug in the barrel jack from the battery pack (6xAA) into the raspirobotboard, the Pi powers up but even if i leave it on for 15min+ i still can't ssh into it. When i try to ping it i simply get 'destination host unreachable'.

Any idea what might be causing this?
I did run 'sudo iwconfig wlan0 power off' to turn off the power management on the wifi. But that didn't change anything.

When the pi is being powered by its usb i can turn the led's on and off and got the 'False' reply when testing the switch.