HP-71b does not turn on when using batteries

[hpcalcuser83]

I have a 71b that will not turn when using batteries. When I use an AC adapter it will power on fine. I checked the battery terminals and they are fine. I checked the DC voltage with a multimeter and it is fine until I place the last of the 4 batteries in such that it touches the terminal (4 batteries in line will measure 6 VDC until I insert the last battery an it touches the terminal - then the voltage measures 4 VDC or less). Anyone ever experience this?
-Gil