Rechargeable (NI-CAD) "N" Cells spotted


Available Radio Shack under the Radio Shack brand, first time I have seen.


What about the cells for an HP-97?
They look awfully like regular size C, don't they?

Does anybody know how to rebuild these? Can I replace these cells?

Gil Petri.


The HP-97 battery pack uses four "sub-C" batteries. Radio Shack sells them with solder tabs.


What is the "mAh"? Does it make a difference or it's just how much the battery will last?
Will the HP-97 use 1500mAh or what?

Thanks in advance,
Gil Petri.


mAH is the capacity of the cell. A cell rated at (say) 75 mAH can supply 75mA for one hour.

Well, actually it's not that simple. the mAH rating is generally based on a 4 hour sidcharge (from memory) do this cell could give you 18.75mA for 4 hours. At 75mA it would actually give you slightly less than 1 hour service.

You'll also find rates specified as 1C 0.5C, 10C, etc. These relate to a current of that multiple of the capacity of the cell. So 1C would be 75mA, 0.5C is 37.5mA, and 10C is 750mA (for the example above). The C notation is very commonly used for describing charging rates, and for describing the characteristics of a family of cells.

AA cels were typically 400 to 450 mAH in the days that the HP41 was born. These days I can go out and get 1100mAH AA nicads.

The same is true (but to a lesser extent) with the sub C size. I can't remember the figures off hand, but 2300maH (2.3AH) seems to ring a bell. The newer, higher capacity cells will give you longer running time from a single charge, but a charge will take proportionally longer.

The best indication of a full charge is a rapid rise in temperature. I once posted the temperature of a full HP97 pack as I charged it. The rapid rise in temperature indicated to me that a 24 hour charge was WAY too long.

It's also important to note that higher capacity NiCads are more sensitive to overcharging.

If you look carefully into nucads, you'll find that they make nicads for rapid charge/discharge, trickle charge, etc. They vary in capacity since the use characteristics (partially) determine how they need to be constructed and where the tradeoffs in terms of capacity vs. ruggedness need to be made.


I had the local Battery Patrol (I believe they have changed to Interstate Battery.) rebuild one last spring. Cost was only $15.


You'll find that many small appliances (like cordless telephones) use packs made up of several N size batteries. Many used to be nicad, these days they tend to be NiMH.

Look for replacements and tear them apart. :-)

It may be a cheaper alternative.

And yes, for the 97 (and HP 41 printer, cassette drive, disk drive, etc) the correct cell is the SubC.

If Radio Shack AKA Tandy are anything like they are here, I would avoid them like the plague for buying anything. They are twice the price of normal electronics shops, and even they are twice the price you pay if you know where to go!

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