Hello, I noticed your conversation involving our batteries and wanted to offer some assistance. First and foremost, all lead-acid batteries can vent gas that is both toxic and flammable, regardless of whether or not they are "sealed" or "maintenance-free." The Camry hybrid battery is located in the trunk and needs to be properly-vented to the outside air, as do any batteries that are located in any enclosed space in a vehicle. The D34M BlueTop and D34 YellowTop mentioned in this thread, do not have provisions for external venting (both batteries are identical internally).
The DS46B24R YellowTop for the Prius does have a vent port, where an external vent hose can be attached, although I do not believe that battery meets or exceeds the OEM specs for the Camry. While a venting scenario is rare and may be unlikely to happen, we cannot recommend placing any battery is an enclosed location, unless it can be safely vented to the outside air.
In addition to our DS46B24R, our Group 27, 31, 34C, 51 and 78 batteries all have provisions for external venting, but we would consider all of those batteries to be custom fitments in a Camry Hybrid and special modifications may be needed to accommodate them. If anyone has any questions about our batteries, I'll do my best to answer them.
eCare Manager, OPTIMA Batteries, Inc.