HP 35 - Working with AC Charger but not Battery Pack

[Steve Simpkin]

To add to the above description. It’s a bit hard to see but when you unplug the charger cable from the calculator two tabs on the metal bar shown in the photo below short the outer two pins together which connects the battery to the calculator electronics. Any corrosion at the point where the tabs contact the outer pins will also prevent it from working with the batteries.