I used to roadrace a Corvette, and always ran it easily 4 hours or so
with a battery only and without a problem with a point-type ignition
(and brake lights) and several to a dozen or so restarts during the
course of a race and/or weekend. Of course no electric fuel pumps or
computers to deal with in those days.
No alternator means another horsepower or so available, fewer failure
points, no mounting issues, it's not in the way of something else, etc.
If the ignition system requires 16 volts to work properly, I'd say
somebody mis-designed the system, knowing that typical automotive
batteries are only 12-14 volts, and can drop a couple to several volts
below this during starting.
If it was me, I'd run two strong batteries, and monitor the voltage
periodically while starting and running, and recharge every day or two.
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