I got my HP-27. It did not have any of the problems that the seller said it had. Must have been related to the tiny bit of corrosion on the tip of the battery contacts.
I cleaned that off and it worked. All except the decimal points, which were always on. So, I opened it up to see what the problem might be. After I put it back together it worked 100%. Lucky!
However, while it was open, I noticed something odd. There was a trace that was cut. Was this just a factory modification (change)? Are all 27s like this? Could this be something that a previous owner did? Why?
Everything seems to work 100%. It even charges properly. The trace comes from the AC Adapter pin.
Here is the photo of the cut trace: