Conventional flooded batteries are commonly used for boats and require the periodic addition of water to the battery cells. Modern gel batteries do not need maintenance and typically last longer.
Flooded batteries are also called lead-acid batteries. They are usually less expensive than gel batteries, but they can leak, and boat owners must periodically add water to keep the electrolyte level above the cell's plates to keep the battery functioning properly, according to "Selecting A Marine Battery" by Joel Brady.
Modern gelled-electrolyte, or gel, batteries are sealed to prevent leakage and spills. They also lose less charge over time and provide enough power for quick starts. They are also more resistant to corrosion, shock and vibration.
Unlike gel batteries, flooded batteries are classified as hazardous for transportation purposes. However, the cost of a gel battery is about twice that of a flooded battery.
