Battery Issues

[Jerry B.]

I’d like some help concerning a current issue with batteries for my HP-35 and HP-67 calculators. I’ve been using battery packs marketed online by Mark Hoskins and been very pleased with their performance, but he has recommended me to this forum for tech help.

Some history, in case it’s important:

Both calculators use the same battery pack, so I bought one for each of them in August 2015 (usually good for at least 3 yrs, which has been found to be true). In case it matters, the 35 was bought new with its charger in 1974. The 67 was bought new with its charger in 1979 and was refurbished by HP when its card reader wore out. It’s been my experience that the 35 will function without the battery installed when used on the charger, but the 67 MUST have the battery installed even when using the charger.

The current issues:

HP-35

When I checked the 35’s battery voltage with my volt meter it read 4.26 volts, even though the battery pack was labeled 3.6 volts. Strange! I plugged in its charger without the battery installed, turned it on, and the display showed faint flashing numbers (similar to the 67 when performing its calculations). I put the battery back in the 35 and plugged in the charger but got the same display only brighter. The battery compartment is pristine, with no corrosion.

HP-67

The 67’s battery obviously died and was discarded. I installed the remaining battery without the charger, turned it on, and the display showed it was ready to use as usual (no “red dot” indicating a low battery). But when I put it on its charger with the battery installed and turned it on, the display showed a bright flickering “0.00” and a bright red dot. The battery compartment is pristine, with no corrosion.

Any comments are appreciated.
Jerry B.