AGM batteries VS Flooded batteries?
Flooded Batteries.
Flooded or "wet cell" batteries are the most commonly used batteries on the market today. Flooded batteries come in the widest variety of shapes and sizes due to their widespread usage in a multitude of industries and applications. Flooded batteries again use lead plates, a sulphuric acid electrolyte, and plate separators but that is where it stops. Usually flooded batteries are not sealed, and do not recombine the gases to liquids internally. Instead, these gases are vented externally. Internal gases produced are released directly to the environment. Through these same vents can flow acid, steam, and condensation, leading to maintenance. Flooded batteries do require maintenance, in the form of water, to routinely replenish lost electrolyte through the vents. Lead plates start to deteriorate when they touch the atmosphere, so if you fail to maintain these batteries, they will corrode and fail. Flooded batteries hold very good rates of charge for the price, but require more work. Unfortunately due to the internal construction, flooded batteries have the weakest internal construction, and some very high internal resistance statistics. Flooded batteries have the advantage of being significantly less expensive, but they require adequate ventilation, maintenance, and also have the potential liability of tipping or spilling.
AGM Batteries.
AGM batteries technology was originally developed in 1985 during the cold war for military aircraft where power, weight, safety, and reliability were paramount considerations.
For most situations AGM (Absorbed Glass Mat) batteries is the safest and best option by far. AGM batteries require no maintenance. There is no need for ventilation and they will not spill.
Technically speaking; AGM batteries are "recombinant" – which means; the Oxygen and Hydrogen recombine inside the battery. These use gas phase transfer of oxygen to the negative plates to recombine them back into water while charging and prevent the loss of water through electrolysis. The recombining is typically 99+% efficient, so almost no water is lost.
Charging voltages for most AGM batteries are the same as for a standard type batteries so there is no need for special charging adjustments or problems with incompatible chargers or charge controls. The leading advantage is that they charge up to five times faster than flooded batteries, and the ability to deep cycle. AGM batteries offer a depth-of-discharge (DOD) of 80 percent; where flooded batteries on the other hand are specified at 50 percent DOD to attain the same cycle life as AGM batteries. Since the internal resistance is extremely low, there is almost no heating in AGM batteries. Even under heavy charge and discharge currents. AGM batteries are capable of delivering higher currents on demand. They also out last flooded batteries at by at least three times - even when deep-cycled.
AGM batteries stand up well to low temperatures and have a low self-discharge rate (from 1% to 3% per month). So they can sit in storage for much longer periods without charging. The plates in AGM batteries are tightly packed and rigidly mounted (sandwich construction), and will withstand shock and vibration better than any flooded batteries.
AGM batteries are typically heavier than flooded batteries due to the volume of lead plates. In most instances, the heavier a battery is (more lead), the better its quality - comparing it with the same amp-hours. Hence AGM batteries are more expensive per amp-hour compared to flooded batteries.