Apparently AGM batteries have several advantages over conventional batteries. I'm considering using an AGM battery (e.g., the Bosch S6) as a replacement in my '02 XJR.

I would be interested to hear from those with experience as to whether there are any disadvantages (other than the higher price) of an AGM battery?

For those totally unfamiliar with AGM battery technology, here's a brief descrioption from Consumer Reports: "Absorbed glass mat (AGM) batteries contain a very sparing amount of acid electrolyte, have a sealed case, and use a different internal chemistry that reabsorbs loose hydrogen molecules that react back into water. That combination eliminates the need to replenish electrolytes, extending the battery’s life span. These batteries are more forgiving of “deep discharge,” ... , which coats the lead plate electrodes with sulfate deposits, [and] can reduce the life span of a conventional battery by a third or more. That makes AGMs a good option for absent-minded drivers or for vehicles that regularly sit unused Many higher-end vehicles come with an AGM battery; never replace an original-equipment AGM battery with another type, because the toxic gases vented or electrolytes leaked by non-AGM batteries may be dangerous if the battery is mounted in the trunk or passenger compartment."

It seems that venting an AGM battery may be less of an issue than venting a conventional battery in trunk mount situations such as ours. Do AGM batteries even have vent holes, for example? How important do you think it is to vent the battery in an X308, either conventional or AGM batteries? BTW, the conventional battery that I've had in the car for more than 6 years has never been vented -- every part of the battery is clean and dry with no sign of any corrosion on or around the battery -- just my experience; not trying to make a case pro or con venting. Thanks for any feedback, Al.

 

Al,
I put an AGM on my XJ8 when I did the mechanical restoration on it fall of 2018. I would've put an Optima in it but they don't make one that size and I didn't feel like fabbing up a bracket at the time. I got my battery at Advance Auto Parts, but a Die Hard would be the identical battery except for the sticker.
So far so good as far as reliability. I would expect this battery to last 7-8 years or even longer, between the AGM technology and the sheltered location of the battery.
-Steve-

 

I've run an AGM battery for 4 years with no problems. I thought about setting up its vent, since there's a grommet in the battery area designed to run a vent tube through, but I didn't have the hoses and couplers and never got around to it. Haven't noticed any issues from that.

 

Going just over two years with the Walmart (Everstart brand) AGM H8 battery and all is well. I have the vent tube attached, but AGM batteries are only supposed to vent in a dire emergency (like a shorted cell), unlike normal flooded cell batteries that vent slightly all the time while in operation.