The Museum of HP Calculators

HP Forum Archive 10

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Battery/Charger usage
Message #1 Posted by Silvio on 1 Feb 2003, 7:02 p.m.

Hi all.

I have a question on the use of AC Adapter/Chargers. I have a 41CX that I use at the office and a 41C at home, both have a rechargeable 82120A battery pack in very good condition, and holding charge for relatively long periods. Will I damage the calculators if I use the charger all the time? Will it damage the batteries?


Re: Battery/Charger usage
Message #2 Posted by Vieira, Luiz C. (Brazil) on 1 Feb 2003, 8:52 p.m.,
in response to message #1 by Silvio

Hi, Silvio; tudo bem? (are you well?)

This is not a complete reference, but I believe it is a good starting point; I would appreciate extra comments, suggestions and mostly corrections.

Based on what I know and have heard about, NiCad's and NiMH have different behavior when recharging cycles are the issue. AFAIK, NiCad's should never be used till their charge (ddp and load current) is nearly exhausted, meaning they should not be connected to the load for longer than it's recharging demand. Otherwise there are some "dangers" (not destructive) related to the so called "memória de carga" (I do not know the name of it in English, but this is the effect observed when charging cycles happen too frequently, mostly before proper time, and the batteries get "used to" that behavior) observed in the NiCad's. Based on these facts, allowing the batteries to discharge till the equipment signals this fact is the procedure I'm adopting so far. If I am using the equipment (calculator, printer, any NiCad operated portable) and it signals Low Battery condition, I promptly connect it to the AC adapter and let it connected for as long as stated in its manual/guide. I avoid using the charger for periods in time longer than the necessary to fully recharge the batteries. I read that NiMH batteries are a bit different, because they do not have the "memory" effect and may be recovered when nearly exhausted.

The only equipment I saw that has a different charging procedure is the 9114B disk drive, but it uses an acid-composed battery (like automotive batteries) and this is another story: they better be floating around their operating voltage for as long as they can be.

Hope this helps. And please, guys, add whatever needed to complete this information, O.K.?

Luiz C. Vieira

Re: Battery/Charger usage
Message #3 Posted by Jon Ibarra on 2 Feb 2003, 4:34 p.m.,
in response to message #2 by Vieira, Luiz C. (Brazil)

NiMH batteries have less memory effect than NiCd but I´m affraid they also have. So it is recommended to discharge them as much as possible before charging again. I think LiIon batteries (used mainly in handy phones) have no memory effect but I´m not sure.


Jon Ibarra

Re: Battery/Charger usage
Message #4 Posted by David Smith on 2 Feb 2003, 4:45 p.m.,
in response to message #1 by Silvio

It is always best to not leave batteries on charge for extended periods. The HP91/92/97 in particular dump a lot of current into a pack and it will get quite warm... a good indication of a full charge. The 82120A is not as bad, but longest battery life will occur if it is not overly charged. With NiCad batteries you should use them until they are discharged before recharging.

Re: Battery/Charger usage - Thanks
Message #5 Posted by Silvio on 2 Feb 2003, 6:04 p.m.,
in response to message #1 by Silvio

Thank you all. Apparently it is a bad idea to just let the calculators connected to the charger all the time. I'll have to remember to disconnect the machines every day before came home, or keep using the regular alkaline batteries.

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