There are two aspects:
1) in most cases the backup battery (if discharged and/or at end of life) will still have a few millivolts left
2) a short between the contacts means in other words a very low resistance between the contact
a discharged battery will have a low resistance, but higher than a short
if there is no battery at all, you will have a very high resistance between the contacts and thus a undefined potential
Considering the Newt to measure this voltage with relatively high impedance you have the solution.
Johannes
-----Ursprüngliche Nachricht-----
Von: Frank Gruendel [SMTP:Frank_Gruendel_at_t-online.de]
Gesendet am: 14 December 2001 02:05
An: newtontalk_at_newtontalk.net
Betreff: [NTLK] Re - Backup Battery Instl
>When the backup battery is installed plus (flat) side out, I get an
>error message (backup battery is dead or missing). When I put it in plus
>side inward, I don't get the error message. What's up with that?
When you install plus side inwards, you create a short between the
battery contacts. No harm will be done, but the Newton will measure a
voltage of zero volts instead of the voltage remaining in your backup
battery.
If you put the backup battery in the correct (plus side outwards) way,
the Newton can measure what voltage is supplied from the battery.
Observant people will think about why a completely empty backup battery
(resulting in a voltage of zero volts, too) wouldn't result in the
same behavior as putting the battery in the wrong way. I can't answer
that, but 0 volts caused by a short between the battery terminals is
electrically different from 0 volts due to no voltage being
supplied to the terminals, I guess the Newton must somehow notice the
difference.
Frank
Newton software and hardware stuff at www.pda-soft.de
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