The battery has failed...(high resistance). The reverse polarity is due to
the other batteries and load still being connected... This happens on ups
equipment that has not been well maintained poor batteries. When a load is
called for you end up with 300-400v backwards across a single block as the
current demand ramps up reasonably quickly there have been some spectacular
results.... !

Steve

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
Jinx
Sent: 16 October 2008 02:21
To: Microcontroller discussion list - Public.
Subject: [EE] Battery flipped polarity

Just doing some maintenance on a device and notice that one battery
out of three is no good

It's a prototype product, based on a 12F675 powered by 3 AAA
alkalines

For the vast portion of the day the PIC is sleeping and using next to no
current. Only for less than a second a day is it required to do any work,
and draws just a few mA for that time. I predicted that the batteries
should last close to their 10 year shelf life

This one has been running fine for over 2 years, but stopped working
a couple of days ago. Not expecting it to be the batteries I checked
connections, sensor etc. Apart having from a little verdigris and a spider
web (it's installed in a sheltered spot outside) the circuit seems OK and
does still work

Two of the batteries measure 1.48V, the third measures -0.2V

Any ideas what may have caused this ?

Also, is something like WD40 or CRC going to be alright as an after-
spray to prevent verdigris (and spiders) ?

TIA

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