I have two almost identical PB 520c. One is more banged up, with 20 mb
RAM and OS 8.1. The other is in great condition, with 36 mb RAM and OS
7.6.1, but I can't get either to run off battery power. They both
recognize and charge one of my batteries, but won't run off it alone,
or boot from it. Makes them a lot less usable.
EZ