http://en.wikipedia.org/wiki/VRLA_battery said:AGM automobile batteries are typically about twice the price of flooded-cell batteries in a given BCI size group; gel batteries as much as five times greater. Less reliable than flooded lead acid 
- Longer recharge time than flooded lead-acid
- "Sealed" batteries cannot tolerate overcharging: overcharging leads to premature failure.
- Shorter useful life.