I thought I was having problems with mine as well so I switched out batteries and managed to squeeze some life out of the unit. Then I googled the specs for the AP51. Maybe it's me but why are we using a 6vdc battery deck for what appears to be a 12vdc device? Even the AC adapter has a 12vdc output. Could it be that 6vdc is the lower threshold for the AP51 and its not the connector at all?
You can buy Nickel-Zinc (NiZn) AA sized batteries that are rated for 1.65vdc each ( X 4 = 6.6vdc ) but I think that level is still insufficient and that the AP51 should have come with a 12vdc deck instead of the 6.
Here's the specs I found for the AP51. Voltage spec is toward the bottom of the page:
http://www.alfa.com.tw/in/front/bin/ptdetail.phtml?Part=AP51&Category=105479
I picked up a couple of low profile 12v sealed lead acid batteries this afternoon from Batteries Plus to do a DIY replacement. I'm hoping it will do the trick.
