HP 11c chg batteries, not working


Ack...the batteries in my favorite calculator died. Purchased three new SO 1.5v replacements. Put them in and nothing. Ran through the battery replacement troubleshooting script ...nothing. What happened?



I once had a 17B that had a broken battery clip. When I installed the new batteries, the unit did not turn on. Fearing that I completely broke the battery connection, I took the unit apart. It was then that I noticed I had placed the batteries in backwards. Glued the unit back together, turned the batteries around and it worked fine.



there is one keyboard sequence (operation) that is suggested in the HP11C manual in the case the calculator do not respond to keystrokes: simultaneously press [ON] and [D] (or [yx] key). If the calculator 'reacts', chances are that the number in the display is unreadable and you need to press the [<-] (left-arrow, or backwards) key.

About batteries, there is also a suggestion in the manual: use a piece of conductive wire and briefly connect both positive and negative battery connectors with each other. In order to avoid electrostatic discharge and damage your HP11C, do not remove the batteries. A brief shorting will not damage the batteries.

A third option is checking all batteries one at a time. I once found one N-cell in an HP41 that had an interesting behavior. All batteries measured about 1.45 to 1.49 Volts, but the calculator briefly flash a 0.0000 and turned itself off. I tested each battery for current with a 45 ohms load resistor, brief contact. One of the batteries barely indicated some current, and when connected to the resistor its terminal voltage dropped to less than .7 Volts.

Maybe after either a brief short in the batteries terminals or using three undoubtedly fresh batteries your HP11C will be back to business.


Luiz (Brazil)


the battery posts are clean and appear to be structurally intact. I have followed the troubleshooting guidelines to a "T" a few times now (ON and y^x, short the terminals)

I tested the new batteries on a DMM. All three batteries ring 1.56 +/-

argh. is the calculator worth "servicing" vs buying new?



Hi, Jane;

I'd not take a "last shot" considering service for now. One last suggestion: as it seems you have knowledge about electricity (mentioning a DMM and shorting terminals), believe me when I tell you that even when electrical terminals look clean, cleaning them may help solving the problem. MOS-based, portable devices, as all LCD-type HP calculators, consume such a few power that the few µamps necessary to power them up may be reduced to a lower amount by thin coats of dust or even human fat, resulting in bad contact. I am sure that you were carefull enough making a good check, but gently rubbing the contacts with a swab moisted (not dripping) with alcohol (dry it right after) may also solve the problem.

Let us know if you succeed or if you need guidance. If service is needed, chances are you'll find someone close to you that's able to repair it. Unfortunately, HP no longer supports Voyagers (HP10C, 11C, 15C and 16C).


Luiz (Brazil)


"...consume such a few power that the few µamps necessary to power them up may be reduced to a lower amount by thin coats of dust or even human fat..."

I thought it would have been around the other way. Modelling the dust/fat as a resistance, very low current means very little voltage drop across the resistor. I'd have thought that a low power device should handle higher resistances then a higher powered one.


Hi, dot;

I agree with you when "linear", pure resistance is considered. I am not actually sure if this is the case here. Human fat is not also a pure insulating material because of the organic and composite saline found on it. But in many circumstances, after trying to turn some Pioneers and Voyagers on without success, simply spinning batteries around their axle with the thumb or removing and inserting them back was enough to bring the calculators back to business. In fact, having these "MOS-based units" being design with low current, low power consumption in mind, batteries and related connectors are not exactly design to handle high current, so they do not need higher physical pressure to keep their contacts with the lowest resistance possible. You can compare Voyagers battery contacts with the golden platted battery contacts found in Classics and higher current devices, like Topcats (HP9x), printers and tape drivers. They are designed to bent when battery is inserted, providing lower-resistance contact surfaces and allowing higher current, hence lower voltage drop.

Thank you for pointing this fact out, and please, I'd like knowing if my reasoning fails somehow. I am always interested on discussing technology and, mostly, unusual situation. Any other comments? Anyone?


Luiz (Brazil)

Edited: 16 Sept 2004, 12:28 a.m.


The telephone company designs their analog circuits so that a small current is always flowing through the wires, even when idle. They found that without the current, splices and other mechanical connections would develop a thin layer of corrosion, causing circuit degradation and outages.


Hi Jane,

Currently, 11c units in working condition go on e-bay for between $90 and $150 routinely, and in perfect condition with manuals, for more than that!

So, yes, it is worth fixing in that sense.

Or swapping etc.

May we ask you to describe why the 11c is your favorite? Is it out of long experience and familiarity (with ignorance of other designs) or have you come to that feeling through experience with other calculator designs?

There have been many interesting discussions regarding design and ergonomics, man-machine interface, aesthetics, tactile aesthetics etc here, and your input will be both appreciated and enjoyed!

Best regards,


Edited: 15 Sept 2004, 3:07 p.m.


well, i think i need to go the service route. cleaned all the batteries and battery contacts. took the back cover off too and tested for loose connections around the battery area. i'm at loss. dang.

bill - my affection towards the 11c is akin to a toddler's desire of his favorite stuffed animal. Been using the 11c, problem free, since the mid 80's. If I had to put my finger on something, it would be the stack manipulation.


I would consider using fixthatcalc.com to have it repaired or consider a new HP33s. If you go the new route, you could probably sell your 11c for something to help you pay for a new Hp.

The Hp12c is the basic same layout as your 11c and works nearly the same if you don't need trig. However number correction is not as nice ie a backspace on the 11c will clear the whole number on the 12c.


amazon (quick search) sells the hp33s for $47

fixthatcalc charges flat rate of $59 plus shipping, if it's repairable. If non-repairable, I'm out $29

It doesn't seem worth repairing a 20 year old calculator for $60!


If you don't want to fix it, can you sell it? I need another HP-11C to fix one I have that have a broken LCD.

Please mail me in private (take out the capital letters from my address above)

Best regards,

123456 to delete


Once you use the 33S you might just change your mind...


Hi Jane,

I understand your feelings. I too used one from 1982 through 1995, when I lost it on an airplane. (replaced it with a 32sii which I was very happy with--more powerful in every way than the 11c for 1/2 the price at the time).

When I suddenly became a "collector" 1-1/2 years ago, I bought an 11c again and it was very much like "coming home".

Now that I have used a whole range of these HP calculators, I think I can make a few observations which may or may not be helpful to you.

If you do a lot of programming, then the 32s (and 32sii) is much nicer than the 11c. And, the 33s has yet even more power, as it has the equivalent of 7 kb of 32s memory. The 33s is great for memory!

If you find that you need to solve "equations" or "expressions" but do not need a looping capability, then again, the 32sii and the 33s are better in that you have a built-in algebraic expression interpreter. (Of course they also have RPN programming as well so you can do looping if you want).

Note also that the 11c does not have a built-in solver routine. The 32s, 32sii and 33s have a solver.

However, if you do not take advantage of the programming capability of the 11c, but rather do manual things, and you like the ergonomics of the stack functions, then you will be greatly disappointed by the 33s. The 32s and the 32sii will not disappoint you so much here, although stuff is in a different location. The 33s has the stack buttons scattered all over the place.

The 32s is the same as the 32sii expcept that it is older and does not have the following:
kg-->lb, in-->cm, fahr--celcius conversions, roll up (R up), equation capability, fraction entry and display capability. But, the 32s menu system is more logical than the 32sii--there is a bit of "cramming" in the 32sii and in attempting to keep as much of the 32sii arrgt as possible, some things are not quite so smoothly organized in the arrangement.

The 33s has all of the conversions that the 32sii has, plus some "constants". However, there are three significant bugs in the built-in functions:
1. rectangular to polar conversion
2. decimal hours --> H.ms conversion.
3. Reset does not properly reset RAD to DEG setting but removes RAD annunciator.

Fortunately, for the first two bugs, it is possible to input robust, small program routines to return the correct answers--developed here on the Forum by a guy called "Norris".

The 3rd bug merely requires vigilance after a reset!

I hope this information helps you.

Ironically, by becoming a collector, I have now opened my eyes up to all the other possibilities--and so now I see regular RPN in a much less favorable light than I once did. I am now very happy to have an editable algebraic command line for instance. I find this superior for so much work--as you can see and check, or later modify, a solution, rather than retyping everything. This is also greatly helpful when doing sums--as you have a record of the input to check! Much faster than re-doing! In other words, the Algebraic command line machines, including most sharp "PC" series, and the HP 30s, and some of the Casios, are really great---better even. Sharps are even programmable.

If you like RPN and HP, and you are not needing trigonometry, then I recommend the 17bii, which is RPN and has an algebraic solver, and as such, effectively has an editable command-line parser. If you go into the solver and type "X=" and then the expression you want to solve, you can then solve for "x' and you get the answer--and it goes to teh stack as well. (The big downer on the 32sii and 33s is that the equation list is not editable!!!).

I like the 17bii perhaps more than any other HP in fact, for genereal non-geometry use. (And there are some clever solver routines for the trigs available).

Best regards,



Edited: 16 Sept 2004, 11:28 a.m.


I have a friend in my office who has a 15C which simply refuses to operate on the Silver Oxide button cell batteries, but which works fine with the alkaline button cells (eg. LR44). Strange behavior, since I also have a 15C, and my calculator doesn't seem to mind if it's using alkaline or silver oxide. We checked everything, cleaned the contacts & the battery faces, cleared & reset his calculator, and even did the momentary short-circuit across the battery contacts, but his 15C still refused to run on the silver oxide cells. Ultimately, we just traded batteries - he got my alkaline cells, I got his silver oxides, and both calculators seem to be happy. Are there any other people out there that have seen one of these Voyagers refuse to work on Silver Oxide cells?


hmmm...the old batteries were the LR44s. I can't recall what the batteries before then. Oddly, even the manual states the SOs would be ok. i'll give it a shot. thanks.


Well, folks, remember that different battery formulations MUST have different cell potentials, even if very similar. If the calculator was (accidentally??) designed to be fussy about power input, then you will have to just stick with the mercury cells or whatever it was designed with in mind.

There is no true equivalence here, only strong similarities (or not, as in this case).


Same thing happened to my 11C 10 years ago. One day it just wouldn't turn on anymore. Fortunately I was able to get one of the last 15C's available at the bookstore. Now the 11C just sits in a drawer thinking of the good old days..


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