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HP Forum Archive 08

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Lithium packs for display and storage
Message #1 Posted by Michael Meyer on 23 July 2002, 7:02 p.m.

I've been building battery packs lately with Eveready AA lithium batteries. For the HP-35 type, I glue three together, lightly grind the terminals and solder appropriately, and then use doll house copper ribbon wire to make the metal sheet contact between the outer cells. They solder quickly and easily and with low temp and no vents appear to be covered. These batteries have a ten-year shelf life, and from what I've read, may be useable beyond 20 years. They are supposed to be leak-proof as well. I like that I can store the calculators in my collection with the rechargeable batteries removed and can still turn them on, use them, and not have to worry about charging them. These batteries have about 5 times the life of alkaline batteries and have a much wider range of temperature stability. I know there's been discussion here about voltage differences, but I think it's minimal enough that I've encountered no problems and have read of no problems on the forum.

I'd be happy to post photos if anyone is interested...



Re: Lithium packs for display and storage
Message #2 Posted by David Smith on 23 July 2002, 8:51 p.m.,
in response to message #1 by Michael Meyer

Make damn sure that nobody plugs in a charger with one of them installed... otherwise a small nuclear scale explosion may await.

Also NO commecial battery is leakproof. The same manufacturer also says that their "N" cells are leak proof. I have quite a pile of hopelessly corroded HP41 battery contacts that say otherwise.

It is always best to store a machine without the batteries installed. If you keep the pack near the machine then double bag it. The gasses and fluids that they will eventually belch and spew can be deadly to ones precious machines.

Re: Lithium packs for display and storage
Message #3 Posted by Michael Meyer on 23 July 2002, 9:04 p.m.,
in response to message #2 by David Smith

Thanks for the "heads-up". I also wonder if keeping power on a circuit for many years can result in oxidation of the circuit by electrolysis, as suggested by Victor Toth.

Since I started collecting and rebuilding, I've left the rebuilt packs in the calculators. I now plan to remove them all and store them separately.

Just wondering, though, out of ignorance, what toxic gases a lithium cell could release? I thought lithium cells were pretty air-tight to prevent H2O from reacting with the lithium. But I don't know.

Anyone know how safe these cells are, in terms of leakage? I know not to try to charge them.... and no one in my home is allowed to even touch my collection.


Re: Lithium packs for display and storage
Message #4 Posted by Ellis Easley on 23 July 2002, 11:17 p.m.,
in response to message #3 by Michael Meyer

I first met lithium batteries when the IBM PC/AT came out and, of course, I had to see what was inside the black box. There were two cells (the unit was 6V) which were hermetically sealed (no vents). I cut one open and a fuming liquid came out. I assumed there was metallic lithium in there and got a little freaked out by the liquid - it actually gave off a mist - so I wrapped it up in a bunch of paper towels and threw it in a metal garbage container - I figured the main thing was not too let it come into contact with water, because of the lithium - and prayed that it didn't start a fire. (It didn't)

Are these 1.5V lithium cells? I think I've seen such a thing, I would like to know how they get 1.5V since the other lithum cells seem to be either 3.0 or 3.6V nominal - maybe they have a built in electronic regulator? A series regulator would waste half the available power but would let you offer a AA replacement with long shelf life and high capacity. Could also be a step-down switcher in there, the only bulky part might be the inductor - that would have better efficiency and so would deliver more of the available power (even longer life).

Most regular batteries leak because they have to have a pressure relief vent to release the hydrogen that is generated if they are discharged too fast. There is an oxidizer inside to react the hydrogen to water and if the discharge rate is never too high, the pressure never gets high enough to activate the vent. I don't know if the chemistry in lithium cells involves hydrogen - or if there really is metallic lithium inside. One type of lithium cell has a name ("Li SO2") that suggests sulfur dioxide is one of the chemicals inside - that might explain the fuming I saw, although I don't remember smelling sulfur dioxide.

Re: Lithium packs for display and storage
Message #5 Posted by Michael Meyer on 24 July 2002, 12:55 a.m.,
in response to message #4 by Ellis Easley

Thanks. I, too, have wondered how they get 1.5 volts. I've been buying these, though, in 4 packs at Office Depot for $8.99. More expensive, of course, but if they equal 20 regular alkalines, store better, etc., they've seemed very worth it. I do suspect metallic lithium as the cells are so light. (Maybe it just means they don't need much lithium to have big amounts of energy...)

It makes sense that these batteries are fully sealed come to think about it. Sooo...

I'd still bet that these cells could sit in a calculator for several decades safely. But why take the risk....

I do keep a pair in my HP-25 and the three in my daily HP-67. I've run these for countless sessions with no sign of them letting up! I'll let you know if I have any problems. Let's check back in 20 years and see... <grin>


Re: Lithium packs for display and storage
Message #6 Posted by Juergen Rodenkirchen (Germany) on 24 July 2002, 5:52 a.m.,
in response to message #5 by Michael Meyer

As this thread made me concerned on storing battery packs in general, what about Ni-Cd packs? How long would you expect a (discharged) Ni-Cd akku pack can be savely stored without showing unwanted or harmful effects? Besides, what would you recommend on storing those? (If these questions should be stupid in a way, please accept my apology being not very skilled in HW-things ...).

Re: Lithium packs for display and storage
Message #7 Posted by Ellis Easley on 24 July 2002, 1:48 p.m.,
in response to message #6 by Juergen Rodenkirchen (Germany)

Most NiCads seem to leak eventually - although my HP97 that I got this Spring has its original 1977 battery in it and shows no sign of corrosion or leakage. I got a set of 4 "N" NiCads to use in my HP41C about two years ago, I've only charged them three times (very gently) and one of them has the white crystals forming around the positive terminal. Here is a very good article on the subject of battery leakage and corrosion in calculators from Viktor Toth's website:

The usual explanation for leakage is pressure buildup caused by the temperature increase that occurs if an aggressive (non-trickle) charging current continues to be applied after the cell is fully charged. One type of "smart" charging circuit has a thermistor mounted in the battery pack to sense the temperature and stop the full charging current once the temperature starts rising quickly.

But I have the N cells and also two Classic batteries I bought brand new from EduCalc (for the used HP75/printer/disk drive set they sold) which I only charged a few times, which I stored away from the calculator (no external leakage current), which leaked over the years anyway. So I have two theories about NiCad leakage: (1) they might tend to leak less if they are used regularly - sitting idle for extended periods after complete self-discharge, they seem to leak even though they are not subjected to overcharging. (2) Smaller cells (N, AA) seem to leak more than sub-C's - in the case of normal use and occasional overcharging, this would make sense since the smaller volume would reach a higher pressure after a shorter period of abuse.

I wish Nicads came with something to absorb and/or neutralize the electrolyte that escapes, like the felt rings for car battery posts - those work very well.

Re: Lithium packs for display and storage
Message #8 Posted by Juergen Rodenkirchen (Germany) on 24 July 2002, 2:14 p.m.,
in response to message #7 by Ellis Easley

Ellis, thanks for the comprehensive information! It really helps me a lot as it gives me deeper insight into this matter!

Re: Lithium packs for display and storage
Message #9 Posted by David Smith on 24 July 2002, 12:27 p.m.,
in response to message #5 by Michael Meyer

There are many different types of lithium chemistry available in batteries lithium-sulpher dioxide, -manganese, -thionyl chloride, -iodine, etc. Each has its own characteristics and output voltage. I think the 1.5V cells are manganese.

Unless your battery is like a space or implant qualified hermetically sealed unit (think hundreds or thousands of bucks each) then it has a seal in it of some sort. Also some kind of pressure vent seal. And as we all know from our engineering courses ALL seals leak, eventually.

Re: Lithium packs for display and storage
Message #10 Posted by Michael Meyer on 24 July 2002, 10:31 p.m.,
in response to message #9 by David Smith

I do believe that they CAN leak, but I'm still guessing it's rare. Let's ask: has anyone had a lithium (non-rechargeable) battery leak (Camera battery, etc.)?

NiCd's seem to leak with regularity, as do all the older NiMH batteries I've collected. Nearly all alkaline cells have leaked over the years if stored in items... I did find a pristine set of alkaline batteries (luckily) in an old calculator. Might be of interest to a flashlight collector or something... 25 year-old AA alkalines....

The non-rechargeable cells seem to leak when they become completely discharged, which would (again) take ten to twenty years if lithium's were stored. I swear I don't have any stock in these things, and certainly don't want to be blamed if they DO leak-- or find out the hard way myself-- but I am (still) guessing they're the safest to keep in something long-term....


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