Hi dave87rs, OPTIMA batteries actually have a lower self-discharge rate than traditional, flooded batteries, so they can hold a charge when not in use longer than flooded batteries. However, it's always good practice to either use a battery maintainer or disconnect your battery if you know a vehicle is going to sit idle for an extended period of time. When batteries are discharged below 12.4 volts and allowed to sit in that state for an extended period of time, sulfation begins to diminish both performance and longevity.
Ekpolk, even though our batteries have a “sealed” design, all lead-acid batteries can vent gas. Under normal operating conditions, an AGM battery will not vent gas. Since alternators or chargers can fail, the safest and correct mounting method for trunks and passenger compartments is to make sure that any possible gas venting will escape to the outside of the vehicle. All vehicles with original equipment battery locations in the trunks or passenger compartments will have a vent provision that should be used.
Our group 27, 51, 34C, and 31 batteries all have ports for connecting a vent hose. Although people do it anyway, we would never recommend installing an unvented battery in any enclosed space, because there's a legitimate, albeit unlikely, safety risk involved.
For example, IF there is a voltage regulator failure, and IF the battery is severely overcharged, and IF this goes unnoticed, and IF the battery vents because the internal pressure exceeds the release pressure of the vents, the gasses are both flammable and toxic. This may sound like a lot of “ifs,” but attorneys and engineers get paid to plan for every worst-case scenario. If anyone has any other questions about our batteries, please don't hesitate to ask.
Jim McIlvaine
eCare Manager, OPTIMA Batteries, Inc.
www.facebook.com/optimabatteries