HP 11C low battery indicator



I have recently received a HP 11C with almost flat batteries. When I turned the calculator on, the display was "0.0000". When I started typing in numbers, I have noticed that the numbers that I've typed were masked with "0.0000".

For example:
If I want to type in "12345678.0", the calculator displays:
therefore the first 5 digits are replaced by the "0.0000" mask.

I took the batteries from HP 11C and placed them in my HP 15C. On the HP 15C side, the asterisk sign at the lower left hand corner of the screen started blinking. However, there was no blinking asterisk on the HP 11C side.

I would like to know if there is a version of HP 11C without the low battery indicator or is my HP 11C acting strange?

Thanks in advance,


My personal experience is that many of the old voyagers don't detect a low battery condition properly if at all. However, this is mitigated by the fact that they can go for 20 years without needing new batteries.


Is the shelf life of alkaline, mercury or silver oxide batteries in excess of even 10 years?


Is the shelf life of alkaline, mercury or silver oxide batteries in excess of even 10 years?

The silver oxide (Energizer) is specked at about 7.5 years at 20 degrees C to be at 85% of capacity. It's linear, so after 20 years is should have just enough power to run the calculator. I can't find a spec for the alkaline cells, but it has to be substantially less.

There was a PX675 mercury cell with the same dimensions as the 357/LR44 cell it's voltage is 1.35. The would mean that the calculator would run at about 1 volt below nominal which would have been just ok. These had a shelf life of longer then the silver oxide cells, 10 years to 85% I think but they stopped making them around 20 years ago. Mercury cells have a very flat discharge voltage curve and so would stay at 1.35 volts until the instant they die. Not a good choice for use in a calculator CMOS memory. The only calculator I have that used mercury cells originally is the Sinclair Sovereign.


I have a Sharp PC-1211 Pocket Computer (same as Tandy TRS-80 PC-1) with CMOS memory that uses MR44, 1.35V mercury batteries. It uses 4 batteries and is rated at 5.4 V (4x1.35). These batteries are still available for hearing aids.


Oh yeah. I've got one of those too in the form of a PC-1 and they did use 1.35 volt mercury cells, I forgot I had that. But all mercury cells have been illegal to manufacture for many years, although they still might be available on the internet. The hearing aid batteries that you refer too have been replaced with zinc-air ones. They are 1.35 volts too, but have a much, much shorter shelf life once you activate them. Most hearing aid batteries last 1 month or less once you pull off the little tab blocking the air vent. Some have been engineered to last up to 1 year after activation.

Edited: 30 Sept 2011, 9:46 p.m.


I tried zinc-air on my rapacious HP42s' and usually got 2-3 months in heavy usage.


Amazing. So silver oxide is the way to go. Eveready now has 675 hearing aid batteries which it claims have the longest life, (the package says almost as good as mercury)3-4 years. It does not say what the chemistry is.

I know I burned through a ton of these batteries with my (3) HP42s, so I usually ended up stealing them from my 15C!

Battery life on the 42s was usually less than 6 months with heavy usage- programs, infrared, etc.


The (modern) 675 cells are zinc-air. Zinc-air has an extremely high energy density about 4 times that of silver oxide. The downside is the very high self discharge. If you need run long programs and use your calculator to do so every day they are a much better deal than silver oxide. However, if you mostly let your calculator sit in a draw, silver oxide is defiantly the way to go. Alkaline is a compromise, lower cost than silver oxide but less shelf life.

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