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Using The Gel Car Battery and Marine Gel Batteries In Solar Applications

by Chris - October 19th, 2011.
Filed under: Equipment. Tagged as: , , , , , , , .

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Gel cell batteries are suburb batteries for solar, marine, and automotive applications. The gel car battery as well as marine gel batteries are excellent choices for use in a solar system. This article covers maintenance and installation of the gel cell battery in order to get the longest lifetime out of them.

Gel batteries are categorized as valve regulated lead acid (VRLA) batteries. However, they are more often referred to as sealed lead-acid (SLA) or ‘maintenance free’ batteries. All these terms describe the same characteristics:

  • Acid starved electrolyte
  • Does not need maintenence (e.g. adding water) like flooded cells do
  • Can usually be mounted in any orientation

The acid starved electrolyte is what gives the 12 volt gel battery their superb deep-cycle qualities. When a flooded cell battery is deeply discharged, the negative plates obsorb oxygen and create sulfite crystals on their surface. These crystals insulate the plates, effectively decreasing the active plate area on the battery. Also, when the plates absorb excessive oxygen, they ‘shed material’, which means they literally flake off. In a gel cell battery, the electrolite is ‘starved’. This means that the chemical conversion stops due to the loss of material in the electrolyte rather than encouraging material shedding from the plates. This significantly reduces the damage to the battery during deep discharge.

While both the 12v gel battery and AGM battery are VRLA batteries and both are superb for deep cycle applications, the deep cycle gel battery is more ‘acid starved’ than AGMs. This gives more protection to the plates, and therefore gives gel cell batteries better deep-discharge performance than AGMS. However, AGMs do perform better at low temperatures – below 32 degrees farenheight. This is rarely a problem in most solar or marine applications, but it is an important fact to keep in mind.


Charge and Discharging A 12v Gel Battery

Overcharging and deep discharging of gel batteries is the most common ways they are damaged. Overcharging occurs whenever the battery is charged above 14.1 volts. In fact, a gel battery charger shouldn’t exceed 14.1 volts for charging, and should maintain the battery at 13.8 to 14.1 volts when trickle charging. This is quite a bit lower than flooded or AGM batteries, which are typically maintained at 14.4 volts. For that reason, these batteries often require a gel cell battery charger and are not compatible with most ‘smart chargers’. When in doubt, verify the output voltage of your gel cell battery charger with a multimeter to ensure it is behaving properly.


Discharging is an equally common way that the gel battery is damaged. While avoidance of overchargeing is largly a factor of choosing the right gel battery charger, over discharging will be more directly under your control while you use it in your application. Batteries should never be discharged below 10.5 volts. This is considered 0% state of charge (SOC). Also, it’s important to recharge the your 12 volt gel battery as soon as possible, once it reaches this point. Leaving a 12v gel battery in a deeply discharged state encorages the formation of sulfation crystals and plate shedding. Both of these phenominon irreversably decrease the batteries ability to store energy. While gel batteries have more protection against deep discharging than any other type of lead acid battery, they are not immune.


Extending The Life Of Your Batteries

On the topic of discharging, many people don’t realize that SLA batteries last longer the less they are discharged. For instance, if a battery is only allowed to discharge to 75% SOC, it will last 3.5 times longer than one that is regularly discharged to 20% SOC, according to the table below. This is more an argument to use over sized marine gel batteries rather than an argument to limit the amount of discharging. If you need the full capacity of a 50AH battery in your application, you should gain more than twice the working lifetime if you used a 100AH gel cell battery instead.


marine gel batteries cycle life

Deep cycle gel batteries lifespan vs depth of discharge - table from East Penn



More Information

You can read more details on gel cell batteries on these websites:







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