HP15C CE - Battery problem

[Johnh]

The issue that my calculator had was unchanged with two brand-new identical batteries measuring the same voltage. I can also confirm from measurement, that the positive sides are directly connected to each other. I had wondered about diodes, as in the past linked above, but I also see many references online to direct parallel connection being ok with these batteries due to their internal resistance, based on batteries of the same type and age.

There's a fault inside, but it's working OK now and I decided not to open it all up further to investigate further. But I'll check the batteries again soon.