Maintenance Free Deep Cycle Battery Types
Deep cycle batteries provide a steady electrical current that can be drawn over an extended period of time. They can be discharged down to 20% of their capacity and recharged again without damaging the battery.
They are typically rated in amp-hours. They are the type of battery found in automotive starting batteries, golf carts and solar electric/backup systems.
Sealed Lead Acid (SLA)
These batteries are very popular for UPS systems, engine starting and limited dual-purpose battery applications such as wheelchairs and mobility scooters. They have a closed oxygen cycle and a fixed electrolyte made from sulfuric acid. SLA batteries are known for their long shelf life, but like all batteries they will eventually need to be replaced. Fortunately, with the right battery maintenance techniques, you can extend their useful life.
During a battery charge, oxygen molecules from the negative electrode combine with hydrogen ions from the positive electrode to form water and lead sulfate. As the battery discharges, these ions move back and forth between the electrodes creating an electric current. This process of sulfation degrades the lead in the positive electrode and corrodes the grids on both the positive and negative plates. The battery then becomes less capable of holding a charge.
The’sealed’ aspect of the SLA is due to the battery having a case that prevents the hydrogen gas produced during recombination from venting out. This is also why they have a safety vent to avoid excessive maintenance free deep cycle battery pressure build-up. The sealed case allows SLA batteries to eliminate the need for regular top-ups of distilled water (unlike the flooded lead acid battery, or FLA, subset). However, these batteries require more stringent charging control in order to limit hydrogen production and maintain their maximum capacity.
Valve Regulated Lead Acid (VRLA)
This is a type of rechargeable battery that contains lead-acid cells in series inside a single container. Each cell has two lead plates submerged in a sulfuric acid electrolyte solution. These batteries are commonly referred to as maintenance free because they require no adding of distilled water to the electrolyte.
The cells are sealed and protected by a special glass mat separator or absorbent fiberglass mat (AGM). This prevents the lead plates from making contact with one another, thus eliminating the need for periodic addition of water. The positive and negative plates are sized to have a ratio that allows oxygen to be recombined in the battery, and there is an overflow valve that retains the cell contents regardless of cell position.
In addition, the AGM and gel types have a special additive that suppresses progressive sulfation of the negative electrodes. This extends the HRPSoC cycle life of VRLA batteries compared to conventional flooded lead-acid batteries.
VRLA gel and AGM batteries are leak-proof and can be mounted in any position. They are also more environmentally friendly than flooded batteries since they do not emit gasses on overcharge and there is no need to regularly check and top off water lost through electrolysis. However, they still need inspection and regular functional testing to ensure the performance of the battery.
AGM
AGM batteries don’t leak, are more resistant to shocks and vibration, and have a longer lifespan than standard lead acid. They can also have a lower internal resistance, which lets them charge almost five times as fast as standard batteries gel battery suppliers and also helps them resist sulfation (the process where the sulfuric acid that forms on the battery’s positive plates turns into lead sulfate).
AGMs are built with both potive and negative lead plates sandwiched between ultra-fine fiberglass mats saturated in a mixture of water and sulfuric acid. The mats are then compressed and welded into place. AGMs are also more resistant to damage from heat and vibration, which makes them better for use in a variety of vehicles.
While AGMs are maintenance free, like flooded batteries they still require some care. They should be regularly checked for signs of corrosion and maintained in a cool, dry place away from sunlight and excessive heat. They are also more susceptible to overcharging, so it’s important to use a smart charger that can adjust the charging voltage based on temperature to avoid this problem. It’s also important to regularly use a desulfation charge on your battery to reduce the risk of sulfation and reduce its impact on battery life.
Gel
A gel battery has a Jell-O-like acid mixture that is suspended in silica gel. This prevents movement of the acid, which is a major cause of internal battery damage and short circuits. They also feature one way safety vents in place of the open vents found on wet cell batteries, which reduces gassing during use and charging. This allows gel batteries to be used in any position without fear of leaking.
Unlike AGM or flooded lead acid batteries, gels require no watering. Gels also tolerate excessive discharge much better than flooded or AGM batteries, which makes them ideal for very deep cycle applications. Gel batteries are non-spillable, can be operated in any position, and require low charging voltages. They also don’t sulfate as quickly, so they have a longer lifespan than flooded or AGM batteries.
Regardless of the type of maintenance free lead acid battery you choose, it is important to maintain it properly. This means keeping the battery clean and checking its electrolyte level on a regular basis (do not overfill). It is also recommended that you replace the battery with a new one on a timely basis and keep the charger set to the correct float voltage for the battery. Lastly, it is important to understand that the chemical composition of these batteries makes them more sensitive to heat variations and cycling regimes than their wet cell counterparts.
