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Choosing Rechargeable Batteries for Solar Applications

Whether you’re looking for solar batteries to power your RV, backup system or off-grid home, you need to pick the right type battery and voltage for the job. Selecting the proper rechargeable battery means having a solar-powered system that functions properly with minimal maintenance.

Flooded/Wet Solar Batteries

High-capacity, photovoltaic (PV) batteries are a must for off-grid home and backup system use. In addition to durability, these types of solar panel batteries feature deep cycle technology that operates under even the most challenging outdoor conditions, including variable temperatures.

Flooded (Wet Cell) solar batteries require maintenance, which involves maintaining their water levels and cleaning up corrosion that can occur from spilled acid and gassing. If water levels are properly maintained, the battery can last just as long as AGM and Gel Cell batteries in most cases.

They also have the added benefit of being able to add chemicals in order to extend the battery life. We have seen several positive examples of using chemicals such as our Battery Equaliser when our customers’ batteries are becoming weak. We’ve tested Battery Equaliser paired with various desulfating technology that we carry, and we’ve seen batteries that were out of service brought back to life! If you are seeing the early symptoms of a weaker battery, it is an inexpensive way of trying to restore your battery pack.

Batteries for solar renewable energy applications also feature a rugged exterior design to ensure optimal performance in harsh environmental conditions.

AGM Rechargeable Batteries

Absorbed glass mat, or AGM, are lead acid batteries perfect for use with solar panel systems. Often they are referred to by our customers as a gel battery by mistake because of their non-spill characteristic, but the internal electrolyte of the battery is different. AGMs have a fiberglass matting that surrounds the lead plates. This creates an environment that charges and discharges better.

For high amp draw situations, AGM batteries do have a slight advantage in discharge performance over flooded batteries. For this reason AGMs can get away with a slightly less amp/hr. (AH) rating for applications than flooded batteries. You can work your own example using our Calculator | Sizing a 12 Volt Battery to a Load. In addition to being a safer choice when it comes to corrosion, these rechargeable batteries are a good choice when the system you are powering won’t be operated continuously, or if you cannot be around to monitor a flooded battery’s water levels.

They also have a low discharge rate, so if you need to take your battery pack offline for a few months, they do have the added benefit of a slower discharge rate compared with a flooded battery. The average AGM we carry has a self-discharge rate of approximately 3% a month. That is of course exponential over time, so you don’t want to let them sit too long—but a few months in moderate weather will have very little adverse effect on the battery pack.

Gel Cell Batteries for Renewable Energy Systems

While gel batteries are similar to an AGM variety, it must be used with caution before installing into a solar system. Gel cell batteries contain a silica-type gel that the battery electrolyte is suspended in. This thick paste-like material allows electrons to flow between plates but will not leak from the battery if the case is broken.

Gel battery chargers charge at a slightly lower voltage rate than an AGM or flooded battery, so you need to pair them with a solar charge controller that works for gel batteries, or you can risk heating up the gel electrolyte and damaging the battery. Gel batteries will typically have a lower capacity rating over their AGM and flooded battery counterparts, but they also cycle very deeply.

When it comes to maximizing cost and space when creating a large battery pack, you will find that your cost is more and capacity less, but you also gain the ability to deeply discharge them without harm. You may even find that you need to buy an extra battery, or string of batteries when using gels over their AGM or flooded counterparts in order to achieve the same capacity. If you’re creating a small solar setup consisting of a single battery, or even a couple batteries, and it’s in a warmer climate, a gel battery might make sense for your application. However, you must weigh the cost and the added benefits to see if it makes sense.  

A word of caution: Be sure to use the right battery charger or your gel cell battery won’t perform as expected, and it can even lead to premature failure.

Find out more about AGM and gel cell batteries in our Knowledge Base article, Gel vs AGM: Not Quite the Battle of the Ages, but Nice to Know.


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  • Hi all I was wonder something about solar panels , I have 4 12V deep-cycles battery’s from my boat I put up for winter for about 4 mo. I was wonder what I would need to keep them charge for this long .

    Edwin Cude
    November 3, 2016 a 6:01 pm
    • With solar it a bit of a math problem. You basically need to make up for any parasite draw, and most will design a system capable of put two days of energy back in a single day at a bare minimum. If you have a small to no parasite draw you might be able to get away with a small panel such as a 30 watt, but you won’t know until you do the math. I would recommend reading our article called Solar Systems the Right Way.

      Tech
      January 16, 2017 a 1:45 pm
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