Expected Battery Voltage on DM41L

Discussion of hardware issues related to the DM1x/DM41. Please ensure that you specifiy whether the issue is related to a credit card size unit or a "Voyager" unit (DM1xL/DM41L).
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Rick
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Joined: Sun Jan 10, 2021 2:46 pm

Expected Battery Voltage on DM41L

Post by Rick »

I've just received my new DM41L. Great piece of hardware, but I am puzzled by battery voltage that seems dropping quite fast in my opinion.
The original battery was measuring a little bit more then 2,8V on arrival.
I played with calculator about a hour and a half, trying some math, and loading some programs through USB, and the final voltage was 2,565V.
The day after it was back to 2,611V.
Supposing that the battery was old, I swapped it with a fresh Duracell (new, Expiry in 2030). The initial voltage was 2,977 V.
I used the calculator about two hours on Saturday, and about three hours on Sunday - again with programming, loading through USB and so on.
I ended up with a 2,521V reading. This morning it reads 2,511V.
So I suppose that this battery is almost out, too. I will wait till the end this time in order to see what happens.
However, I'm wondering if my usage is too much, or something is wrong with the device.
Can somebody confirm that such a fast voltage dropping is normal?
I am a little bit worried about battery life expectancy...
Thank you in advance for your opinion and help.
HP-41C, HP-41CV, HP-41CX, HP-48g, HP-50g, HP-11c, HP-15c, WP34S, HP35s, DM41L brand new...
grsbanks
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Re: Expected Battery Voltage on DM41L

Post by grsbanks »

If your DM41L is running firmware V30 then there is a known bug in that version that drains the battery faster than normal.

viewtopic.php?f=12&t=2668
There are only 10 kinds of people in the world: those who understand binary and those who do not.
Rick
Posts: 3
Joined: Sun Jan 10, 2021 2:46 pm

Re: Expected Battery Voltage on DM41L

Post by Rick »

Sorry, I omit to specify this: the firmware is last one - V31.
The calc arrived with this firmware installed.
HP-41C, HP-41CV, HP-41CX, HP-48g, HP-50g, HP-11c, HP-15c, WP34S, HP35s, DM41L brand new...
grsbanks
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Re: Expected Battery Voltage on DM41L

Post by grsbanks »

OK, that one is OK.

Do bear in mind that using the serial port does put a strain on the battery because the calculator does not draw power from USB. Seeing 2.6V after a session of a few hours of what looks like pretty intensive use does not strike me as alarming.

The calculator will keep going even when the battery goes as low as around 2.2V but much lower than that, the "BT" indicator will come on.

Also bear in mind that slightly more power is being taken from the battery when a key is pressed down, which has to be the case to get the voltage read-out, so what you see is necessarily a bit lower than when the machine is sitting there idle.

Finally, you can reduce drain on the battery by switching to 12MHz clock speed instead of 48MHz. However, the machine will, of course, run slower, so in the long run you don't really save much in the way of power because calculations take longer anyway.
There are only 10 kinds of people in the world: those who understand binary and those who do not.
Rick
Posts: 3
Joined: Sun Jan 10, 2021 2:46 pm

Re: Expected Battery Voltage on DM41L

Post by Rick »

Thank you for the info.
I will keep 48Mhz, and go ahead with using the calc in order to see what happens in terms of battery life.
In case I'll be back with the results.
HP-41C, HP-41CV, HP-41CX, HP-48g, HP-50g, HP-11c, HP-15c, WP34S, HP35s, DM41L brand new...
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