On Friday, June 16, 2023 at 9:12:33 AM UTC-4, Erdos wrote:
hi my hp48G's battery is running low. after put fresh set of 3xAAA battery in, I powered on the battery and was prompted to 'recover memory'. I chose 'yes' but the stored memory didn't get restored.
Per an article in the HP Journal from 1991 about the detailed design and operation of the device:
"The 1LT8 chip also monitors the battery voltage. When the voltage falls to between 3.4 and 3.0 volts, the low-battery annunciator is turned on. If the batteries are not changed and the battery voltage falls below 1.5 volts, the system turns off. A 1000-
juF capacitor maintains the VDD supply for several minutes while the batteries are being changed."
If you left the calculator without a full set of batteries for more than a minute or two, you risk memory corruption. I believe that when the calculator wakes up it must do some kind of check on the contents of memory and can discover whether the
memory contents have been damaged. Depending on the level of corruption, you may be able to see some or all directories (but possibly with strange names) and then you could manually move them into directories you newly create. But if there's nothing
after you Try to Recover Memory, you probably have only your backups to get your data back from.
I'm guessing that the capacitor might have a finite lifetime as well; high-capacitance capacitors have delicate internal structures which might degrade, so your time interval during which you have to swap the batteries might be much shorter.
The above is probably true but I hope someone who has actual in-depth knowledge will chime in and deliver actual factuals.
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