I have a TinyScreen+

I am reading the ADC line A4 (thats what appears to be wired up in the schematic), but I am getting a bunch of random values.

Is there any particular trick to obtaining the voltage?

Looks like with the "Plus" version you can only know if it is charging or not..
I'm waiting for a reply on this topic to know more about the options left:
http://forum.tinycircuits.com/index.php?topic=1779.msg3754#msg3754