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
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