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I just received a couple of battery packs from Mark Hoskins (waterhosko)--one Classic size for the 45/65/67, and one HP97 size.

I am wondering if anyone has experience with these packs and can direct me as to proper care of them as compared to the original ones--recommended charging times, how often to cycle them completely, danger of of overcharging and shorting, etc. I have heard from some of you that they are pretty trouble free, but as one so used to NiMHs I have forgotten just how fussy NiCads can be.


Hi Les,

If these are truly ni-cad's and not nimh, then you should charge them up fully, run them down fully and repeat. As a Amateur radio operator of many years, I found that fully exercising the nicads gets the maximum length of usable time from them.

I used to use nicads in my HT'(Handi-talky) and would deliberatly run them down before recharging. Under fairly heavy use, they would easily last 5 years. The best way to kill a ni-cad is to use it to half charge and then re-charge or to keep it on trickle charge all the time. Trickle charge is the worst - after awhile the batteries will only work for a few minutes.

Just fully cycle them and you'll get many years of use out of them.


I completely agree with Bill.

Also, keep in mind that nicads will self-discharge (no use of the calculator) within several months so you need to charge them up fully every 6 months of so. If you let them fully discharge and sit around for a long time they tend to develop internal shorts.

If these are truly ni-cad's and not nimh, then you should charge them up fully, run them down fully and repeat. As a Amateur radio operator of many years, I found that fully exercising the nicads gets the maximum length of usable time from them.

You shouldn't try to completely discharge a nicad battery. It can result in reversed polarity on a cell. The only safe way to do it is to disassemble the battery into its component cells and recondition each cell individually.

You just heard from "la rena de recargables" and a knowledgeable mortal. I have one thing to add. If you totally drain a battery pack with more than two cells in it and let it sit, one of the center cells can reverse it's polarity. I'm not sure what "totally drain" and the time involved in "let it sit" are but that seems to be the story. If you use it like they said, till the calc says to charge it and then give it a full charge, then you will get about 1000 cycles out of it.

So I guess the idea is to use the device until its low battery indicator appears, then charge fully, but avoid draining completely. Ideally, if I don't use the device frequently enough, I should at least try to charge the batteries fully before they drain out completely over time, if I remember.

I fully appreciate the shorting issue. Both my HP97 and and HP41 Printer came with original batteries which presumably hadn't seen use for a long time. Both batteries seemed to work fine for a couple of weeks. Then the low battery indicator started persisting despite given the battery a full charge.


I used to overhaul nicad batteries when I was in the military. One of the problems was that some cells would discharge faster than others, due to age or natural variations in the cells. This led to imbalances among the cells. We would bleed off most of the charge, disassemble the battery, and completely discharge each cell. After testing each cell, and replacing any bad cells, the battery was reassembled and given a full charge. This "balanced" the cells so that they worked in unison.

Look at http://www.buchmann.ca/Article10-Page1.asp for some good tips on using and reconditioning nicads.

This is an interesting article and brings up the difficulties in maintaining ni-cad cells. I have been trying to keep all the calculators in my collection (way too many of them) charged and ready to use/play with, but it's become too much work to maintain the ni-cad cells. So, I've been replacing all of them with the best, longest lasting primary cells made, the Energizer e2 lithium cells.

This is easy to do in the Spice and Woodstock calculators, just swap the AA ni-cad cells for AA lithium cells. For the Classic series I use a modified 3 AAA plastic battery holder: I cut 2 small pieces of thin beryllium-copper sheet metal and melt them into the plastic where the battery pack contacts should be, then solder small wires connecting these metal strips to the battery pack and finish it off with some thick felt padding so that the pack sits in the correct position in the battery compartment.

The end result is a replaceable battery pack that uses AAA primary cells. You can use any type of AAA cell, but the lithium ones have near zero self discharge, don't leak and are very light weight. In addition, lithium cells can supply the current needed to run the card reader and printer (in the HP-10 and HP-19C) and the AAA lithium cells have the capacity of the best ni-cad AA cells. Here's what it looks like:

(I'm working on a way to put AA lithium cells into the Topcats.)

I know that I'm running these calculators at more than the recommended voltage, but only slightly more than a fully charged ni-cad battery pack will produce and I haven't noticed any ill effects having done these swaps with about 30 (mostly HP) calculators so far.


Edited: 9 Jan 2007, 10:49 a.m.

Continuous trickle charge may not be so bad. My shaver has two sub-C nicads in it. Sits on trickle charge continuously. Last time I changed the cells was over 10 years ago. Still runs great (over a week of use while traveling).