At 14:44 31/05/99 +1200, you wrote:
>Davids suggestion about using a MOSFET for reverse polarity
>protection is the best idea by far, but an important thing to note is
>that the N-Chanel Enhancement MOSFET is used "upside down"
>compared to other circuits.  That is to say, the Drain is connected
>to -ve, Source through the load to +ve, and gate to +ve.
>
>When the battery supply is correctly connected the MOSFET is
>biased ON and current flows in the forward direction of the inherent
>Source-Drain diode in the MOSFET.
>
>With reverse battery supply the MOSFET is OFF and the Source-
>Drain diode is blocking.
>
>Should work fine, but use a suitable 3V logic level MOSFET.
>
>Brent
>
>
>Brent Brown
>Electronic Design Solutions &
>HI-TECH Software Reseller
>16 English Street
>Hamilton, New Zealand
>Toll Free: 0508 HITECH (0508 448 324)
>Ph/fax: +64 7 849 0069
>Mobile: 025 334 069
>eMail:  brent.brown@clear.net.nz
>
>

Yes, but requires 2 components and one of them must be very type specific
i.e. N channel 3V FET. This makes this option not cheep in the production
format.
One diode is cheeper and just as effective, the mechanical means that have
been borught up will only sort of work, as you can almost put money on it
that there will be someone that manages to get the small cells in
backwards. The mechanical means is just another level of protection.

Dennis