Good morning/afternoon, depending on where you are!

I don't post much, but I need some advice. I didn't find anything in the search that offered more than I already know. Sorry for the long read, but I know it helps to be completely thorough.

I've had my '04 G35 Coupe 6MT since 2008, and over the last 2-3 years, it hasn't seen as much action, as I bought a daily driver. Recently, when driving longer distances, I noticed a rotten egg smell coming through my vents. After doing some research here and other places, I determined it is coming from the battery. I have an Optima Red Top that is about 5 years old.

I used to drive it regularly enough that my battery wouldn't completely discharge, but over the summer, I let it completely die (lesson learned). Well, I jump-started it and promptly drove it on the freeway for about an hour or so. Noticed the smell start right after driving pretty hard (I'm catless and have been for over 20k, so I know this is not a normal smell). I didn't think anything of it, at the time (I read it might be the AC from using recirc too much), and I let it sit and discharge, again (I know, I know).

A couple months later, I jump-started it, again, and drove it to my new house (40 mins), and no smell. This time, I hooked up the Griot's Battery Manager IV to keep the battery charged. During this time, the battery did NOT boil over. A week later (this last weekend) I took the car out. Drove about an hour and a half on the freeway, with no issues (I even pushed it a little). About an hour into the drive home (not driving hard), I started getting the smell again. When I got home, I pulled the battery cover, and it was sizzling. Obviously, the battery is toast, or getting close.

I've been reading that this could be as simple as a bad battery, but I've also read that it could be a bad voltage regulator in the alternator. It's obviously charging the battery. Would a bad battery allow itself to overcharge like that if the alternator is feeding it the correct voltage, or would the regulator have to be bad? I work M-F, so it will be a while before I will be able to get the alternator tested. I also don't want to drop $150+ on a new Red Top and then promptly ruin it.

Thoughts?

 

Go get a cheap (less than ten bux) volt/ohm meter. A battery that has been sitting for an hour or more should read about 12.5 -12 volts. Start the car, check it again, it's should read 13.8-14.7 MAX.

If it's over that, you would notice the lights getting bright and other problems. I think, you have a shorted cell in the battery. A quick trip to an autoparts store will let you know also, they can test the charging system, and load test the battery.

 

Thanks, Texas. I'll give that a try. The car has been sitting since Saturday evening, and I just had the misses try starting it. It fired right up with zero struggle, if that helps any. Not sure how fast it would drain with a shorted cell...

 

The worst thing in the world for a battery is to let it get below 11 volts. I will calcify quickly and shorten it's life.

 

For sure. I've already done that a couple times. I definitely know the battery needs to be replaced. At this point, I just need to rule out the possibility of the alternator contributing to the issue. Sounds like that volt meter is the next step.

 

Sounds like your battery is toast and on the verge of MAKING toast. I believe if the Optimas are allowed to completely discharge something inside of them gets whacked and they can never get back to full capacity. At least that's what happened to me - left town for a month and killed a red-top. It wouldn't hold a charge for any period of time after that. Switched to and Odyssey Extreme and got myself a trickle charger to keep it happy...

 

Tty doing a load test? My battery voltage tested good, but I knew something was up, since it choked a little firing it up. My alternator went out a week later, lol. That's only cause of the bearings though.

 

Haven't done a load test. I can say it's held its charge for a few days, now, though. I've started it a couple times, just be be sure. Going to pick up a new battery and swap it, though (the guy at the parts shop is a friend, and he'll warranty it out if it ends up being the alt). The guy at the Nissan dealer says it could be the ECU. He said the voltage is electronically regulated.

 

I suppose I should update with my results... 11 months later... It was indeed a bad battery. Thank you everyone!

 

A five year old battery hardly used and allowed to fully discharge is done.
Purchase a new battery!
After replacing the battery use your multi meter to measure the voltage across the battery with the engine running. If it measures 14.4v then your alternator is fine.
Good luck