[rotorwrench]

Absorbent glass mat and gel cell technologies are both considered to be a maintenance free but they are very different technologies. The AGM allowed the cells to be rolled up into a cylinder so that's what made the Optima. The gel cell types are problematic since they are picky about the environment they like to work in and they just don't seem to have the capacity of the AGM. Both are expensive to produce but the AGM is less expensive than the gel cell and has better and more consistent capacity and reliability. The standard old wet cell batteries are still the least expensive to produce and have a reasonable life expectancy but they require maintenance and folks don't like to maintain them.