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HP-50g Backup Battery
12-16-2020, 05:16 PM
Post: #1
HP-50g Backup Battery
How can I tell when my HP-50g Backup Battery (a CR2032) needs to be replaced (as opposed to my main batteries)?

The low battery annunciator, the ((.)) on the top line, and the accompanying "Low Battery(s)" message are non-specific and the none of the HP-50g manuals specify whether they refer to just the main batteries (4x AAA) being low or that either the main batteries or the backup battery is low.

If the low battery warnings come on when the backup battery is the one that is low (without mentioning which batteries it's talking about), I think it's talking about the 4 AAA main batteries which are the batteries most likely to be low, and I remove my main batteries to replace them, then I would have no good batteries in my calculator & lose everything in memory.
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12-16-2020, 08:34 PM
Post: #2
RE: HP-50g Backup Battery
Plug in the USB cable and change all of the batteries (one type at a time). This doesn't answer your question, but it does answer the real question, if you know what I mean. ;-)

--Bob Prosperi
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12-16-2020, 09:53 PM
Post: #3
RE: HP-50g Backup Battery
if you insert new AA batteries (or charged if rechargeable) and the warning persists, then the backup battery will be discharged.

Hardware: Hp48S - Hp50g (5x black + 1 blue) - HP39gII - Hp27s - Casio fx-CG50
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12-17-2020, 01:06 AM
Post: #4
RE: HP-50g Backup Battery
and make sure you backup everything to SD card first Smile

I use both the builtin ARCHIVE and ARCHIV for that.


There are BTMON and BATST utilities available; I think they only monitor the AAA batteries, but a voltage reading there would tell you whether they were OK: if they are, then the flag must be for the CR2032 backup.

Some people recommend changing one AAA cell at a time, not all four at once.

The Quick Start Guide says: "When the low battery annunciator appears, please change your AAA batteries", which implies that there's no annunciator for the backup battery. But I'm not sure that's right. However, the User's Guide says a screen message will appear when the backup battery is low, which seems to contradict that.

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12-17-2020, 05:03 AM
Post: #5
RE: HP-50g Backup Battery
On removing buffer battery from calculator & then turning on no low battery annunciator appears - I conclude no back up low battery annunciator.
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12-17-2020, 08:59 AM
Post: #6
RE: HP-50g Backup Battery
As I understand it, there is no annunciator for a depleted memory backup battery, but remember that power is only drawn from the backup battery when the main batteries are either flat or absent. In other words, the backup battery is hardly ever solicited.

CR2032 batteries are not expensive nowadays and they have a really good shelf life. It's a good idea to replace it as a matter of course every couple of years if the main batteries remain installed and are replaced when the low battery annunciator shows.

As for the suggestion to replace the AAA batteries one at a time... Yes. Main power is then only interrupted for a matter of a few seconds before the fresh battery is installed, and there's every chance that memory contents will be retained even if the backup battery is dead. Most HP calculators behave this way. My HP-71B does anyway, and it's a great idea to have a battery pack ready for a 41C/CV/CX/CL so you can pull one out and install the fresh pack within a matter of seconds.

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