Gel battery is a valve-regulated maintenance-free lead-acid battery. Gel batteries are very strong and versatile. This type of battery produces very little fumes and can be used in places without much ventilation.   How do gel batteries work? A gel battery is a valve-regulated lead-acid battery in which a predetermined amount of electrolyte is mixed with silica fume along with sulfuric acid. This chemical reaction produces a fixed, gel-like substance that gives these batteries their name. Gel batteries are virtually maintenance-free because they use a valve that opens in one direction, allowing the gas inside to recombine into the water, so there's no need to check top up with distilled water or monitor the water level. Gel batteries are very strong and versatile. They can be safely installed in places with restricted ventilation as their gas/smoke production is very low (nearly zero) meaning you can even install batteries in your home.   Special consideration should be given when choosing a charger for gel batteries, as they charge at lower voltages. Overvoltage can cause malfunctions and performance degradation. The term GEL battery is sometimes used to refer to a sealed, maintenance-free battery marked as a setting on the charge controller. This can be confusing and can lead to the wrong charger selection or wrong settings while charging. If other charging methods such as alternators are used, an appropriate voltage regulator must be installed to control the charging voltage. Typical charging voltages for batteries range from 14.0 volts to 14.2 volts, and float voltages range from 13.1 volts to 13.3 volts. Advantages of Gel Batteries Gel batteries are gaining popularity in solar systems for the following reasons:   1.Best for deep cycle applications, typically in the range of 500 to 5000 cycles 2.Maintenance free 3.Spill proof 4.Minimal corrosion and therefore compatible with sensitive electronics 5.Rugged and Vibration Resistant 6.Very safe as there is less risk of sulfuric acid burns 7.Minimum cost per month (cost/months of life) 8.Lowest cost per cycle (cost/life cycle)   Disadvantages of Gel Batteries 1.Can't refill in case of overcharging 2.Requires special charger and voltage regulator   Do not confuse AGM batteries with GEL batteries Today, AGM batteries are often mistaken for gel batteries because of their many similarities.   1.Both are reconstituted - meaning that the oxygen produced on the positive plate is absorbed by the negative plate. Instead of producing hydrogen, the negative plates now produce water, thus maintaining the water content in the battery. That's why AGM and Gel batteries are valve regulated, sealed, spill proof, maintenance free, vibration resistant and can be installed in any location.   2.The notable difference between the two is the difference in electrolytes. The electrolyte used in gel batteries looks like jelly, while the electrolyte in AGM batteries is absorbed in a glass mat that acts like a separator. Due to the properties of the electrolytes used in gel batteries, the batteries lose power quickly at temperatures below 32 degrees Fahrenheit, whereas AGM batteries work efficiently at low temperatures.   3.Gel batteries are best for deep discharge because they are less acid and protect the plates better than AGM batteries. AGM is more compatible where high current is required