Thank you for your post and the update.
I have tried this out but so far have not really been able to replicate it. I have tried connected a battery to the ADC-22, on the LPT port if shows as 1.596V and on the USB as 1.591V. This difference is negligable and does not really count as an offset.
Would it be possible for you to send us a settings file for each of your setups so that we can try it here? Please send them to email@example.com
and I will try again to replicate this issue.