41CX loss of programs & battery removal


I suppose all user programs (no external mem. modules) are lost immediately after battery removal and cannot be saved
if batteries are changed very quickly?

Is this the purpose of the card reader and cards? For storing programs?



If I recall correctly, you can replace the battery and the internal capacitors will preserve the memory content for a good time (some minutes, I think) without the battery. Please correct me if I'm wrong.

Best regards,



On some HP41s, the memory was retained for over 24 hours with the batteries out.



There's a capacitor inside the HP-41

which will protect memory for a

short time while changing batteries.

Since batteries can be changed within a few seconds,

normally no data will be lost.

However, this also is kinda RTFM;-)

AFAIK only the clock of the timer module

or the CX will have to be re-set.

Some of my HP-41s hold memory contents

for a few hours w/o batteries,

but that's not guarateed, of course.

It's always a good thing to have a

data backup on an external medium.

The card reader and the tape drive can be used

to store programs and other data.

You can even do a full backup of your HP-41

to cards or tape.



The 41cx manual simply states that continuous memory may be lost if batteries are left out for an extended period of time. The clock issue is something I was not familiar with so I did some testing. After 90 seconds without the batteries the clock still held the current time. Although continuous memory was preserved, the clock reset to 12:00 AM after 120 seconds wihtout batteries.

Thanks Raymond for the tip


I have a couple of 41CX machines that hold for over a month without batteries. More typical is about a week... as long as you dont press any keys or try to turn them on.


In almost 20 years of using my 41cx regularly, I have never had a memory loss except from a synthetic-programming mistake. The clock and alarms have not been affected by removing the batteries for replacement either.

The first CMOS computer I made, back in 1986, was breadboarded and had a 10uF capacitor from Vcc to ground. After the first day of experimenting with it all working, I shut it down, and was surprised to find the next day that all the RAM data was still intact, held only by the 10uF capacitor. I had not made a backup circuit for it yet to keep the memory alive on battery power while the computer was off.

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