Seriously, if you are the absent-minded type, be careful--you could fry a Mac
serial port or short out your power supply!
More seriously, the cable connectors I am using (9V battery snaps) have exposed
contact surfaces--the pins on the end of the Mini-DIN-8 cable (male end) are
also exposed. If a loose metal object in your briefcase should happen to short
across these, you could wind up with hot batteries, smoke, leakage, etc. This
is especially true if you build an 8-D cell pack. Alkaline D's are rated at
something like 8 amp-hours, with "cold starting power" (surge current) on the
order of 15-20 amps--you could easily weld small stuff like jewelry with this
setup! If this is a special concern for you, the connectors used on model
racing car battery packs are fully insulated--you might want to use those.
Mark