1995 Chevy Impala battery problems

1995 Chevy Impala mileage: 55,000. Hi. My girlfriend's old Impala eats batteries! We had one burst last month, thought it frozen. Got a replacement, now this one is belching sulfurous gasses and is warm to the touch after the car has run for a little while. Not cold enough to freeze, possible charging system problem? Sometimes the interior lights/radio lights go dim, then bright again. The alternator is putting out about 14.7 volts, the battery is charged to about 13.5 volts, seems high. I thought maybe the voltage regulator could be bad, but don't know where it is on that year vehicle! Otherwise a great low-mileage nana car, any advice you guys could give on where to start looking for the problem would be appreciated!