Weird voltages from digital pins

I have been playing around with running an arduino off battery power. When I do this I get weird voltages off the digital pins and off the 5v pins. The battery is at 8.2 volts. Above the 7.4 volts the should cause a drop off in the voltage regulator.

Any help?

More details, please:

What battery? What Arduino? How did you connect the parts? What did you expect to happen? What did happen?

The battery is an array of 6 AA batteries but they have discharged a bit.

The arduino is a combination of 1 mega and 2 unos.

I have wired the positive lead of the batteries into the vin pin (via a homemade splitter) of each arduino and the ground pin of the battery in to the ground pin of each arduino (again via a homemade splitter).

Reading the article about power the ardunio on the arduino website I expected the on-board regulator to drop the voltage so that the arduino would behave like normal (like on a USB cable).

What happened: These are the voltage difference between the following pins: 5v and GND - 2.8v on battery, normal on USB digital pin (HIGH) and GND - 7.16v on battery, normal on USB digital pin (LOW) and GND - 4v on battery, -4v on USB

Something is not right: The batteries should provide about 9V which is OK. Did you check that, too? You cannot have 2.8V at the 5V pin and more than 7V on an output pin at the same time. Please check. On the LOW pin: Did you mean 4V or 0.4V? The latter is OK for a pin driving a load of about 20mA, but not for an unconnected pin. It should read nearly 0V. What is "a combination of" several Arduinos. Can you measure them separately? And what is this "homemade splitter"? You can just connect all Vin pins and GNDs together