Things to Consider Before Storing a Battery
All batteries gradually lose their charge when stored over long periods of time. However, AGM batteries, including high-performance OPTIMA® batteries, lose their charge much more slowly. This helps to prevent the battery from becoming deeply discharged during storage, but it won't completely protect it from damage.
Even when your vehicle is turned off, there still may be a drain on the battery. This is especially true of newer vehicles equipped with computers, alarm systems and clocks that continue to run even when the vehicle is off. Over time, these will drain a battery to voltages too low to start the vehicle. It could even continue to drain to the point of damaging the battery.