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From: csmith@plains.NoDak.edu (Carl Smith)
Newsgroups: comp.sys.hp48.d
Subject: Re: First question.
Message-ID: 
Date: 30 Apr 91 01:48:52 GMT
References:   
Organization: North Dakota State University, Fargo, ND
Lines: 46

In article  frechett@spot.Colorado.EDU (-=Runaway Daemon=-) writes:
>
>I just replaced them.. And two of them
>are 1.2 volts and one is .9.  It is really odd.
>
>       ian
>
>-=Runaway Daemon=-

I have replaced the batteries in my HP28S three times now, and each time
something similar to this has happend.   I got my 28S in December, about a
year and a half ago.  In late January, a month later, the battery indicator
came on, so I replaced the batteries with 3 fresh N cells.  I checked the
old batteries and two measured 1.29 volts, and the third measured 0.45
volts. As a test I placed a 10 ohm power resistor across each cell, to put
a heavy load on them.  Two still measured at 1.1 and the third quickly
dropped to near zero.   This shows that the two cells were still near full
charge capacity.

About two months later, at the end of March, the battery indicator came on
once again.  So I replaced them with one fresh N cell and the two good ones
from the previous set.   The ones I took out measured at about 1.0 volts for
two of them, and the third measured about 0.3 volts, each with a 10 ohm power
resistor across them for a load.

I then took notice that the dead one in each case was the one that sits by
itself.  So I looked at the calculator to see if there was some connection to
the metal piece on the battery door, so that the single battery could be
drained faster than the others.  I could see no such connection.   It looks
like the three batteries are in series.  Therefore there should not be any
more drain on one battery than the others, and no reason for one to go dead
faster than the others.

That third set of batteries, the set that contained one new battery and the
two good ones from the set that came in the calculator ran for almost exactly
one year.  They were put in in late March a year ago, and the battery indicator
came on in late March about a month ago.   So I pulled the batteries and tested
them, to find two good and one dead.   The two good ones included the fresh one
put in a year ago, and one of the two that were good from the first set.  I
replaced the one dead one and the calculator and it is still going.

The third set doesn't prove anything, since the batteries each had been used
different lengths of time before they were put together.  But the first two
sets were brand new batteries, and two came out good and one dead...

This was discussed a while back, but nobody came up with a solution.