Have you got a voltmeter.?
Check the output of the pack. If its low or non existent, you can check back through the cells to see where the problem lies.
Does the AA pack clip up to a pp3 battery clip. If so make sure the + and - are the right way round.
It may be that you're crushing the connector when you put the AA pack in, those pp3 connectors are crap. Try it outside the halo.