Texas TI-58C: (in)famous constant memory issues

[jebem]

External Power Adapter/Charger and Battery Pack information:


According to the official TI site, the TI-58C should use:
- Battery Pack to use: BP-1A
- Adapter/Charger to use: AC9131.

The "Appendix A" from the official Texas "Personal Programming Owner's Manual for TI Programmable 58C/59", 1977, 1979, PN:1034157-1, ISBN 0-89512-027-5 also confirms the above information.
Additional information taken from the above manual:

- CAUTION: The calculator can be damaged if the charger/adapter is connected without the battery pack installed.
- The battery pack needs at least 4 hours to a full charge when the calculator is powered off, or about 10 hours when it is powered on.
- A fully charged battery pack allows for about 2 to 3 hours of continuous operation.
- Under normal use, the rechargeable battery pack have a life of 2 to 3 years or about 500 to 1000 recharge cycles.
- The battery pack can lose its storage capacity if it is not allowed to discharge occasionally. For maximum battery life, it is recommended that you operate the calculator as a portable device at least twice a month, allowing the batteries to mostly discharge, then recharge accordingly.
- Repeated occurrences of excessive battery discharging will permanently damage the battery pack.

The BP-1A battery pack includes three Ni-Cd rechargeable battery cells, for a total of 3.6VDC and a capacity of about 600mAh.
My battery pack contains three cells, each one printed with the reference "188-8134 ASM IN MEXICO".

- The Adapter/Charger AC9131 to be used with the TI-58C, should have an output of 3.3VAC at 500 mA, accordingly to various sites in the Internet.
Here and here and here and here
I do not have one, so I can't confirm that output value, but it seems that a value between 3.3VAC RMS (4.6VDC open circuit) and 5VAC RMS (7VDC open circuit) should be acceptable.
The adapter should indeed output an AC current because the calculator includes a full wave bridge rectifier and a bleeding resistor to limit the batteries charging current.