Providing some type of venting or air circulation for AGM batteries in confined spaces is probably a good idea. It seems to be done in vehicles where the battery is mounted in the trunk. While AGM batteries don't usually produce gas, they can under some conditions.
Recently, I had to replace the trunk mounted battery on my older BMW. The original was the usual "no-maintenance" battery. It had a vent port that attaches to a small tube running to the outside of the car. The new AGM battery I installed also had a connection for the vent tube. This type of venting connection may not be found on batteries intended to be mounted under the hood versus in the trunk. Nonetheless, AGM batteries do have vents and this should be considered when mounting them in confined spaces.
