Rechargable AAA cells on HP-71B?


Hello, all --

I recently got an 82059D "Battery Charger" and AC Adaptor. Only my HP-71B can use it, but I may acquire other devices that can.

It seems as though the 82059D will not charge the cells in a HP-71B, so there is no particular benefit to installing four expensive rechargable AAA cells in a 71B. ($13 for 4x NiCd @ 300 mAh ; $20 for 4x NiMH @ 700 mAh).

The HP-71 owner's manual states the following on p. 271:

"When connected to a power outlet, the HP-71 uses the batteries as a backup power supply and normally doesn't draw any power from them."

"You won't damage the HP-71 by using the computer without batteries..."

This is quite different from the early HP calculators with rechargables. I'd even doubt that rechargable AAA cells were available in 1984, when the HP-71 was introduced. One certainly wouldn't want the HP-71 to try to recharge the cells, if disposables were installed as originally intended.

I measured about 3.6 Vdc across the battery terminals with no battery installed, and the 82059D connected and energized. That's less than what a dead 4-cell battery would register, and below the minimum operating voltage.

So, does anyone see any value in powering an HP-71B with rechargable AAA cells, besides not having to replace disposables, or possibly dealing with alkaline-cell leakage?

Also, how do the mAh ratings of AAA alkaline disposables compare to those of the rechargables? I've never seen ratings printed on the packages of disposable AAA cells.

Thanks in advance,

-- KS


Hello, Karl;

since I got the chance to have an HP71B, I use it with rechargeables manily because I thought I'd have to buy disposable batteries too regularly. In fact, I do not use it very often, so I have no comparison base to offer.

The ones I used first were only 250mAh NiCads, and after they were fully charged, the HP71B was able to keep memory contents for about three months without being used. I only checked for battery status in a regular two-week basis. Six months ago I decided to power it with a pack of four 850mAh NiMH, and although I am using it a bit more for these days, it did not show any 'low battery' sign so far. I also have some 1100mAh NiMH that I use with the 48/49 series, because it seems to me they consume significant more power when communicating.

In fact, except for the HP28S and the HP17BII, I use rechargeables in all my HP's with AAA and N cells, and I have not spent any money with regular alkaline nor regular batteries since then. What I also take into account is that I am not disposing batteries, too...


Luiz (Brazil)


As the HP-71B does not have a recharge function you will not be able to charge rechargeable batteries in it. It is true, that the HP-71B prefers the adapters power 8if plugged in). Then your batteries will not discharge.
You have to charge the rechargable AAA´s in an external charger...


I don't remember for sure, but it seems my 71 went nearly a year on a set of alkalines even when I was using it a lot, in spite of the five extra modules (HPIL, 96KB RAM, 64KB RAM, Forth/Assembler, and Math) and heavy use of HPIL. I fully trust rechargeables not to ever leak when the low-battery indicator is still off and the "Install by..." label on the battery gives a date that is still well into the future.

The reason others have given here for using rechargeables in the 41 was the card reader with its motor and the bar code wand with its light. (Hmmm... I think there was an IR printer-interface module too.) The 71's card reader however has no motor, and no one here has mentioned having a bar code reader that plugs into their 71 so I assume almost none were sold.

Edited: 20 Mar 2006, 3:08 a.m.


hi karl,

for some reason, i've been unable to run my 71b at all on rechargables. it must be that these cells don't make the voltage and my 71 is sensitive enough for it to make a difference.


Hi, Hugh --

For some reason, I've been unable to run my 71B at all on rechargables. It must be that these cells don't make the voltage and my 71 is sensitive enough for it to make a difference.

You have probably stated the best reason not to use rechargable AAA cells on the HP-71B. I'm fairly sure that standard ones are 1.2 Vdc. However, I got intermittent "BAT" warnings when powering it up recently, then got a "Memory Lost" after installing the HP-IL.

Each of the "old" cells measured 1.42 Vdc.

So, I can't explain how Luiz has been successful, unless his 71B is more tolerant or his rechargable cells are 1.5 Vdc.

As for the other contributors, I concur with the assessment of non-rechargability by the 71B.

-- KS


Hi Karl, all;

I'll check the serial # and post about it later (I'm at the University right now, will be back home after 11:30PM today). Maybe my unit belongs to a lote that has a different power supply circuitry. Based on manual contents, the HP71B can use rechargeables, so I did not consider it failling in this case. And the ones I use are indeed in the 1.2Vcc range, but I'll also measure the batteries today later.


Luiz (Brazil)

Edited: 20 Mar 2006, 4:52 p.m.


Hi all;

After getting back home: serial# is USA 2711A0****
The unit is complete with extra 2×4KRAM modules, card reader and HPIL unit (I keep the IL unit in off state.). The batteries measured in the range 1.21Vcc to 1.25Vcc. And I thought I kept the NiMH, 1100mAh pack in the unit, but I actually did not. I remember now that a month ago I bought a Sony 'intelligent charger', and I decided to give the litle NiCads 250mAh a last shot. It is now going to the second month, and the BAT annunciator is still off.


Luiz (Brazil)

Edited: 20 Mar 2006, 11:53 p.m.


Hi, Luiz --

serial# is USA 2711A0**** The unit is complete with extra 2×4KRAM modules, card reader and HPIL unit...

The 1987 serial number indicates that it is newer than mine, which lacks a serial-number stamp, but has the September 1983 "1BBBB" ROM, and came with Ver. C manuals printed in April 1984.

Yours is probably the 1985 "2CDCC" ROM; this is revealed by the VER$ command. More info about HP-71B ROM versions is found at

Valentin has ardently claimed that an 71B is not truly "complete" without its Math ROM, and can make a solid case for that, based upon developmental history. Unfortunately, the 71B was sold without them. Mine has one 4 kB RAM (82420A), the Math ROM Ver. 1A (5061-7226), Surveying ROM Ver. A (5061-7238), and HP-IL Ver. 1B (82401A).

I'm missing the manual for the Surveying ROM, and it's not included in the MoHPC scans.

I found one minor curiosity: There is an "AC" annunciator that p. 30 the HP-71 Owner's Manual states is "reserved for future use". It does not display when the AC adaptor (82059D) is plugged in. Does the "AC" show when yours is plugged in?

Does anyone own an "HP-71" (not HP-71B) that was depicted and referenced as such in manuals? Maybe that was a pre-production version that was developed further, prior to commercial release.

One final note about this thread: I misspelled "rechargeable"! It didn't look quite right with the first "e" omitted, but I wasn't sure and didn't look it up. My apologies for the bit of misinformation to those whose first language is not English...

-- KS

Edited: 21 Mar 2006, 4:22 a.m.


Hi Karl, all;

I forgot to check the ROM version, will do it later, O.K.? I remember I have already done that when I got it, and if I am not wrong, it is ´1DDDD´.

Although I have no ROM modules for the HP71B, I must agree with Valentin and you because any additional MATH feature in a computing device is always welcome. But I could only have my own HP71B about a year ago, thanks to a great (and somehow absent) contributor of the MoHPC. I consider it as a gift, and I also tried to be fair enough with an HP42S as a 'back gift', if there exists such a thing. At the end, it was almost like two friends exchanging gifts. So, that´s the way I got the chance to have this one, and as it also has so many additional stuff, I cannot dare complaining! d8^)

About manuals: I could only print the basic manuals that come with the MoHPC DVD set, no originals with me, too.

About misspelling recharg(e)able: did not even notice till your call... We, non-native English speakers, may learn anytime, right? And missing keystrokes is not an exclusive priviledge of ours...

I have not yet noticed if the AC annunciator 'lits' when the AC adaptor is connected. Will check for it, too.


Luiz (Brazil)

Edited: 21 Mar 2006, 12:46 p.m.


Hi Karl, all;

although the HP71B I have has a serial# that states it is from 1987, the ROM version is '1BBBB' (I confused with the HP75D, that returns a 'ddddd' string to ver$... Sorry!). I also checked the 'AC' annunciatior and, as expected, it does not lit when the AC adaptor is plugged in (I removed one of the batteries and turnned the HP71B on).

So far, no news.


Luiz (Brazil)


Just a followup on my observation on the HP71B:

You have probably stated the best reason not to use rechargable AAA cells on the HP-71B. I'm fairly sure that standard ones are 1.2 Vdc. However, I got intermittent "BAT" warnings when powering it up recently, then got a "Memory Lost" after installing the HP-IL.

Each of the "old" cells measured 1.42 Vdc.

I checked my HP-48G and HP-49G, each of which use three AAA cells. The 49G displayed "Warning: Low BAT" and did not otherwise function; each cell measured 1.27 V.

I put those into in the 48G, and it worked just fine.

So, it seems that the 48G might work with rechargeables, but there is the slight annoyance of the extra cell. There oughta be a law against devices using three disposable cells that are sold only in packages of two or four. That would include the 28-series, the "real" 48-series, and the original 49G, as a minimum...

-- KS

Edited: 22 Mar 2006, 12:01 a.m.


Hi, Karl;

Interesting; I use rechargeables in all of my 48/49 series, and they've all worked fine with the many NiCAD's and NiMH's I tested. I observed that when charged with the Sony charger (BCG-34HLD), the batteries maintain the calculators working for longer than when I let them charging in regular 'dummy' chargers and follow their charging times.

Just to add this info.


Luiz (Brazil)

Edited: 22 Mar 2006, 1:37 a.m.



I have a brand new HP 48gII (1 week). It came with (3) Panasonic LR03 ALKALINE AAA batteries plus the back-up. I read some reviews on HP-EDUCALC site where the AAAs only last 2 mos. I was considering re-chargeables. Would they work ok for the HP 48gII?

Warmest regards,



Hey, Andy;

my HP48GII uses four 850mAh, NiMH AAA batteries, and they are installed for about three weeks, now. No Low Battery warnings so far.

I confess I tried to find the brand mark on them, but could not identify any, just a big POWERPACK printed on it and many Portuguese inscriptions. Seems to be some sort of OEM battery with local identification. In fact, now I am a bit worried...

I also have a set of four 1100MaH NiMh's that I use with the two early original HP49G, but they are identified as Panasonic HHR-4UP. These ones are able to power my HP49G's for more than three months with regular use. By regular use I mean at least three times a week, not a daily basis.


Luiz (Brazil)



Gracias Amigo. I will see how long the Panasonics last. I may consider using the more powerful batteries used in the SONY Digital cameras. I will just make sure i have my hp39G+ nearby in case of low battery and if that one goes low, i have my trusty HP 11C and 15Cs plus an ole Circular Sliderule-lol

Warmest regards from So. Calif,


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