Wet-cell/flooded-cell batteries have thick lead-based plates that are flooded with an acid electrolyte. This is a highly reliable design — failures normally don’t occur until halfway through their 20-year pro-rated life, at which time the failure mode is most often a short circuit. This situation is not an extreme emergency because any one shorted cell only affects overall reserve time by a very small percentage. However, while they’re very reliable with a long life, there are downsides to wet-cell batteries. They require more safety measures and a space-consuming separate battery room to use.