Recently, after driving my car for a while and returning home, I discovered my battery was hissing from both top cell covers along with a light spattering of battery fluid from these same locations. Is this a sign of overcharging and resulting heat buildup within the battery?

My alternator light doesn't work currently, so I can't tell if I am having a positive or negative charging situation.

Thanks for any ideas, Charles

I had the same problem after putting an Advance Auto reman. alternator on my car,it was ok at idle speed but way overcharged above that.It was apparently more than the regulator could control.I had to replace both,again.

It's being overcharged.
Sounds like you need a new voltage regulator.

AND.......... don't smoke around that hissing battery. That's Hydrogen that's coming outa there.

...and just in case you don't know what a spark and hyrdogen can do:

OK, got to tell my "back in the day" story. Sold a '55 2dr wagon to a friend. A couple of months later I'm guessing it developed a loose battery cable and he went out one morning, put the key in, turned it and BOOM. Blew the hood off the thing. Sheared the hood hinges right off the right side and folded the thing over the driver's fender.

If you still have an OEM style points type external voltage regulator...replace it with a Wells VR715 electronic version.
Much more stable charging system. :yes:

get it out of your car...i had one explode (though nothing as horrendous as a launched hood) it was a total mess for years after... e.g.: initial cleanup, baking soda dousing, soda cleanup, scraping, sanding peeled paint underhood, repainting underhood, delamination of new paint, more cleanup and repainting...etc,etc,etc

get it out, test the alt, replace regulator w/solid state one as stated above, but mostly, get the batt out of the car.

one more great reason for a dry cell, gel cell, you pick 'em, anything but acid filled.

It's probably fixed by now anyway but why remove the battery and risk making sparks?

All he needs to do is open the hood, let it air out a minute or two (IF it's been running) and replace the Voltage Regulator.

...and just in case you don't know what a spark and hyrdogen can do:

Yeah...
BTW, I once had one hissing at me along with dim lights. I got out, opened the hood, and popped the caps off to have a look, and the battery exploded in my face. Seems there was an internal crack between cells or something, that made its own spark inside the battery.
SO glad I was wearing glasses. It did affect my hearing though. I could hear nothing for almost an hour, and not so well since.

Usually though, its an overzealous regulator.

I know that many people think that exploding batteries are somewhat of an urban myth, but it sure can happen. I saw one blow up in my friend's face, and it wasn't pretty. I was standing right next to him when it happened, so it sounded almost like a flashbang going off and there was battery acid and pieces everywhere. Fortunately, there was a fire hose in the garage, so we were able to minimize his injuries and the damage to the car to almost nothing (the acid ruined his clothes... looked like he had been shot with a shotgun :D), but it sure taught me to be careful around car batteries.