Stan,
My understanding of the etymology of "beater" came into sharp focus back in
high school: a buddy of mine inherited his sister's Nissan with approx. 1
bazillion miles on the clock.  He didn't know how to drive a standard, so
frequently his technique was a violent, lurching work in progress.
That car was a beater, i.e. something which can be beaten.
Another good example would be a car driven by a pizza delivery guy.  Any car
used for pizza delivery is subject to abuse of biblical proportions, i.e. a
beater.

Best,
d.
1990 GL -- "Mudskipper"