VERY BAD IDEA.  DO NOT TRY THIS.  On some modern cars disconnecting
the battery with the car running will cause the alternator to go to
full field and pump 50 Volts or more through the system, which will
toast all the electronics to a crispy golden brown.

 Yours might not, but do you really want to risk it?  If it wrecks
the Computer or burns up the main wiring harness, it's scrapyard time
- it can easily do damage severe enough that it would cost more to fix
than the car is worth.

 People get away with this dumb trick on their car, then they think
they can do it to anyone's, which is a recipe for total disaster.

 If you want to see if the alternator is charging, get a good digital
voltmeter and watch the voltage at the battery terminals.  With the
car running at a high idle (above 2000 RPM) you should see between
13.5 and 14.5 volts at the battery - 15 volts max, and only if it is
very hot outside.

 If the battery is at 12.5 volts or lower, the alternator is not
working.  The bad alternator is not "discharging" the battery, the
electrical loads needed to make the car run are responsible for that.
Engine Management Computer, fuel injection, ignition system, fuel
pump, radiator fan(s), starter, dashboard instruments, dome light,
radio, daytime running lights...

 Takes 20 to 30 amps to keep a modern car running.  If the alternator
isn't supplying the power for all the accessories and systems, the
power needed has to come out of the battery.  And you can only do that
for so long before the well runs dry.

   --<< Bruce >>--