I have a 2007 Suburban with 290,000 miles. I'm on the 3rd or 4th battery. At 247,326 miles, I went with an AGM battery to see if it would last any longer. I had a scare a few months ago when the battery was completely dead. No lights, nothing. Then I looked over in the passenger seat and there sat a cigar lighter plug in heated blanket still plugged in! Whoever is selling such a thing should be sued into bankruptcy. I hooked it up to my Genius G3500 charger and after many, many hours, it was back to 100% and holding.

Every time I open the hood, the battery plugs are popped out partially. They are under the battery stickers, otherwise, they'd be fully blown out. The battery has vent ports on both ends so I'm at a loss as to why this is happening. Anyone else every seen or heard of this happening in an AGM battery?

 

It's producing too much gas. Maybe it's overcharging. Watch the voltage.

 

AGM batteries are supposed to recombine and reabsorb the hydrogen and oxygen produced during operation. They also have a valve inside that opens at 1.5 PSI to vent any gases produced too quickly by overcharging to be recombined and reabsorbed. I data logged the suburban while trying to hunt down another issue and the voltage didn't show any signs of being too high.

Either the plugs are too loose or it's overcharging at times and not venting properly. I need to check and make sure the vent ports aren't plugged. Mud daubers around here love to plug any tiny little hole they can find with eggs and mud. If that's not it, I'll try just capturing voltage for an extended period of drive time to see if I can catch and overcharge condition.