An Odyssey absorbed glass mat battery does not ever need any venting, but it can and will open its valves if it's damaged or reverse polarized. Optima batteries are not AGM AFAIK, so they would need a vent for safety/insurance. Braille makes the best AGM super lightweight battery, but they're a little more expensive than Odyssey. Others will chime in and list what the parent companies are for Odyssey and Braille, so you could get their non-branded batteries for cheaper.
