Wet Cell, or Flooded batteries 
                            are the most common lead-acid battery 
                            in use today. Wet cell deep cycle batteries are one 
                            of the best storage solutions for the average Off 
                            grid system. They can be forgiving to a point 
                            and are not as delicate as the Gel 
                            and AGM's when it comes to 
                            an overcharge situation. The cost and life cycle is 
                            certainly lower than the alternatives. Wet cell deep 
                            cycle batteries have thick lead plates that are alloyed 
                            with antimony, and are flooded with an electrolyte 
                            and water mix.
                            
                            The electrolyte levels must be checked monthly and 
                            topped off with distilled water. Wet cell batteries 
                            can be ruined by not maintaining proper electrolyte 
                            levels. Wet cell batteries should never be installed 
                            in living areas, and should be stored in a compartment 
                            with ventilation. This is due to the gas that is given 
                            off as a natural result of charging. High quality 
                            deep-cycle wet cell batteries will offer good performance 
                            and are available in many dimensional sizes and Ah 
                            capacities. 
                       
                        
                      A gel cell is a VRLA lead-acid 
                        battery with a gelified electrolyte.
                        VRLA stands for valve-regulated lead-acid and is the designation 
                        for low-maintenance lead-acid rechargeable batteries. 
                        Because of their construction, VRLA batteries do not require 
                        regular addition of water to the cells. 
                        VRLA batteries are commonly further classified as:
                        • Absorbent glass mat battery
                        • Gel battery
                     
                        
                     Gel cell batteries are often referred to 
                      as sealed lead-acid (SLA) batteries due 
                      to their non-leaking containers, but they are not completely 
                      sealed, the valve regulation system allows gas to be expelled. 
                      Unlike a traditional wet cell lead-acid battery, 
                      these batteries do not need to be kept upright and are non-spillable, 
                      therefore can be operated in virtually any position. However 
                      installation upside down is not recommended.
                          As Gel cells are sealed and cannot be re-filled with 
                          electrolyte, controlling the rate of charge is very 
                          important, they are prone to damage if gassing is allowed 
                          to occur.
                          They must be charged at a slower rate (C/20) to prevent 
                          excess gas from damaging the cells. Gel cells use slightly 
                          lower charging voltages than flooded cells and thus 
                          the set-points for charging equipment have to be adjusted. 
                          Most good quality inverters commonly used in solar 
                          electric systems can be set to limit charging 
                          current to the batteries. Gel cells can be used in virtually 
                          any flooded wet cell application (in conjunction with 
                          well-regulated charging) as well as applications where 
                          wet cells cannot be used.
                          Because of their unique features and benefits, gel cells 
                          are particularly well suited for:
                          
                          • Deep Cycle Deep Discharge Applications (Portable 
                          Power, Electronics, Solar Applications)
                          • Standby and Emergency Backup Applications (UPS, 
                          Emergency Lighting)
                          • Unusual and Demanding Applications (Air-transported 
                          equipment, Marine Starting)
                        
                        
                        
                      Absorbed Glass Mat (AGM) batteries are the latest step 
                        in the evolution of lead-acid batteries. 
                        AGM 's are typically VRLA, valve-regulated lead-acid and 
                        are a type of low-maintenance lead-acid rechargeable 
                        battery. Because of their construction, VRLA 
                        batteries do not require regular addition of water to 
                        the cells.
                        VRLA batteries are commonly further classified as: 
                        • Absorbent glass mat battery
                        • Gel battery
                      
                     
                         Instead of using a gel, an AGM uses 
                          a fiberglass like separator to hold the electrolyte 
                          in place. These types of batteries have all the advantages 
                          of gel cell batteries, but can take much more abuse. 
                          They are also called "starved electrolyte", 
                          as the mat is about 95% saturated rather than fully 
                          soaked. That means that they will not leak acid even 
                          if broken.
                        
                          Some advantages over gel cells and flooded deep cycle 
                            batteries:
                            • they cannot spill, even if broken, as all 
                            electrolyte (acid) is contained in the glass mats. 
                            In addition, since there is no liquid to freeze and 
                            expand, they are practically immune from freezing 
                            damage.
                            • charging voltages are the same as for any 
                            standard battery - no need for any special adjustments 
                            or problems with incompatible chargers or charge controls.
                            • low self-discharge - from 1% to 3% per month 
                            is usual. This means that they can sit in storage 
                            for much longer periods without charging than standard 
                            batteries.
                            
                            Basically, an AGM can do anything a gel cell can, 
                            only better. However, since they are also sealed, 
                            charging has to be controlled carefully or they can 
                            be ruined. AGM batteries are superior for marine and 
                            RV applications.
                          
                      
                        
Practically all solar batteries used in PV systems 
                          and most backup systems are lead-acid type batteries, 
                          this includes the standard flooded wet cell battery, 
                          dry gel/dry cell, sealed and agm (absorbed 
                          glass mat). A deep-cycle battery is designed to deliver 
                          a consistent voltage as the battery discharges and can 
                          be charged with a lower current than regular batteries 
                          making them ideal for solar system set ups.