Battery Venting

[BozDMAX]

Noticed the engine was slow to start a couple of times today and this evening got a whiff of a slightly caustic, sulfer-type smell. Truck normally charges at about 14V on the panel meter, but was running closer to 12.5.

Opened the hood wiith engine running and confirmed the alternator was charging at 12.5 on the driver side battery. Passenger side battery a bit lower but we could see the vent cap venting smoke.

Batteries are OEM, closing in on 4 years old and never had any previous problems. No sign of bulging walls in the battery or cracks in the case. No fluids leaking. When I turned off the truck we could hear a faint bubbling in the passenger battery while it continued to vent.

I don't really like being around bubbling, venting batteries so we left for a while and about 10 minutes later checked and the venting and bubbling had stopped.

Q's:

1) Are the batteries truly wired in parallel, or is one of them for starting and the other for everything else?

2) I suspect a weak cell in the pax side, causing the alternator to 'overcharge' which resulted in the venting. Seem reasonable?

3) I didn't look real close at the vent cover. Can you take that thing off somehow or is it best left alone since it is supposedly maintenance free?

4) How do you check for a weak cell? Disconnect, recharge, and then test voltage?

5) If a single bad cell, best to replace in pairs? With? Several have mentioned Optima Red Tops, but their website doesn't even list a match for the Duramax.

6 Other recommendations?

Thanks

John

[DmaxMaverick]

1. Yes. Truely parallel. The batteries are "always on", and neither has preference over the other, except for location on the cables.

2. Reasonable.

3. Covers are not removable (or not supposed to be). If you manage to get one off, it'll never seal again. Best not to try.

4. Listen for bubbling and smell for odor.

5. Replace in pairs, always (except when one is still new, like less than a year). The highest rated Optima in the size group will work well. Good choice. I use Yellow Tops, so I can't give you an accurate part #.

6. Clean the area VERY well with soda before reinstalling the new batteries. Flush well with fresh water after. If you have any bare metal, or blistered paint, scrub it out and seal it with a rust neutralizer preperation, then paint. The prep will neutralize any remaining acid, and prevent headaches later. Be careful with the terminals. Overtightening will spawn a list of four letter words. You can prep them with dielectric grease for added comfort and corrosion resistance.

[JohnC]

I agree. sounds like the pax battery is pulling the whole system down. I think if you isolate the bad battery you'll see things act more normally. Theroretically, you should charge and load test it, but I doubt if it'll take much of a charge. Sounds like you're past the 3 year warranty. If so, you'll have better long term results if you replace both. The bad one weakens the "good" one (and later, the old one will weaken the new one).

[BozDMAX]

Two new Optima redtops installed. They are slightly smaller which is nice. Works like a champ again.

Autozone - $140/each. Yikes. Hate it when I have to pay for something of quality ;-)

Thanks for the quick reply and advice...