Flooded Lead Acid Batteries: The Best Lead Acid Battery?

scanning: time:2021-09-16 classify:Technology info

Flooded Lead Acid Batteries: The Best Lead Acid battery?

Flooded vs. Sealed Lead-Acid Batteries Pros and Cons

  • Flooded lead-acid batteries are the most cost-effective option, but require regular upkeep, where sealed lead-acid batteries (AGM and Gel) cost more but do not require regular maintenance.

  • AGM batteries resist vibration and can handle higher charge/discharge rates and gel batteries can withstand high temps and work best with slow, deep discharge.


  • This article will focus on the differences between the main lead-acid battery types used in the solar industry. You’ve got flooded lead-acid and sealed lead-acid batteries, and the latter group can be broken down into AGM (absorbent glass mat) and gel batteries.

  • Every battery type has a different purpose and use case, so let’s go over the pros and cons of each.

  • What is a Flooded Lead-Acid Battery?

  • For many years, the flooded lead-acid battery has been the standard in the solar industry. This type of battery is also used in golf carts and forklifts. They are the most cost effective and longest lasting of the lead-acid batteries.

  • Flooded lead-acid batteries contain an electrolyte that is free to move around in the battery encasement. When charged, the battery acid and lead plates react to store electricity.

  • These batteries are meant to be mounted upright so that the electrolyte does not leak out of the caps on top. (Since sealed batteries are…well, sealed, you can mount them in any orientation without fear of them leaking. Not the same for flooded batteries.)

  • While this is the most economic battery on the market, it will only reach its potential lifespan if they are maintained properly. The levels must be checked monthly and topped off with distilled water to ensure the longest possible lifespan.

  • Note: flooded lead-acid batteries release toxic hydrogen gas when charging. They need to be enclosed and vented to the outside to prevent this gas from being trapped and creating a hazardous environment.

What are Sealed Lead-Acid Batteries (AGM or Gel) Batteries?

The sealed lead-acid batteries are very similar to the flooded version, but there is no access to the inside compartment. This means that you do not have to add distilled water. The electrolyte is sealed inside, and there is enough to allow the battery to live out a calculated number of cycles.

The Fullriver DC400-6 can be mounted in any configuration. They won't leak due to the sealed nature of the design.

You sometimes see these referred to as VRLA (valve regulated lead-acid) batteries, because they have a small valve to allow for the escape of the gasses that occur during charging.

What is an AGM (Absorbent Glass Mat) Battery?

Absorbent Glass Mat batteries are the most popular VRLA battery because they can work in a wide range of conditions. The electrolyte is suspended in a thin fiberglass mat that is situated between the lead plates. This allows the battery to be resistant to vibration, which makes them a great choice for RV and other mobile applications.

They can also be mounted in any orientation. It is common to see them mounted on their sides for convenient placement and wiring.

AGM batteries are more expensive than flooded lead-acid batteries, and they do not last quite as long. But for that extra price, you get the luxury of not having to maintain the batteries or deal with as much gas that is released during the charging phase.

They are perfect for mobile applications, places where leaked acid would be problematic, remote locations where maintenance will not be possible on a regular basis, and places where the batteries could be subject to extremely cold temperatures.

What is a Gel Battery?

Gel batteries are another VRLA battery very much like an AGM, but they use a thick paste that allows the magic to happen rather than the fiberglass mat.

The main difference between gel and AGM batteries is the charge rates. AGM batteries can handle higher charge and discharge rates than gel batteries.

Gel batteries are the most costly of the VRLA batteries, but excellent candidates for projects that need a very slow deep discharge. They also last a bit longer in hotter temperatures, so you might pick them if you are concerned about high ambient temperatures in the space where the batteries are enclosed.

Gel batteries are more expensive than other lead-acid battery types, so they are not ideal outside a handful of specific solar applications (very hot climates, mainly). The technology has been eclipsed by other battery types that have been developed more recently.

It is very common for people to mistake a Gel for an AGM, and this can affect the lifespan of the battery. Gel batteries are the most sensitive of the VRLA batteries, and It is critical that the correct charging parameters are used when you have a Gel battery in your application.

My Experience Living Off the Grid

When I first started living off the grid in 1996, I had never heard of a Gel or AGM battery. Everyone I knew that was exploring the off-grid lifestyle used the flooded golf cart batteries. Once I started working in the industry and doing more installations, I started seeing more battery options.

I quickly realized that the bigger flooded batteries called L-16s were the standard in most of our nicer installations. These are sometimes referred to as a forklift battery. While the cost per amp hour was similar to a golf cart battery, it became evident that the L-16s lasted longer. It was explained to me that the bigger the battery, the thicker the lead plates would be, therefore gaining a better lifespan.

About three years ago, my flooded batteries were at the end of their life, and I opted to get AGM batteries this time around. While I don’t really notice much performance difference, I am relieved to not have to crawl under my stairs to check water and maintain the batteries anymore. Even though my L-16s were in a sealed vented compartment, once in a while I would catch a whiff of something that must have been the hydrogen gas seeping out. I haven’t smelled that since, and it was worth every penny to make the switch.

For more advice on which battery type is best suited for your project, chat with one of our system designers or grab a copy of our Solar Battery Guide, or our guide on deep-cycle batteries that covers all you need to know about these stable battery types.


Batteries come in many shapes and sizes. In the solar industry, two battery chemistries work well for our purposes: lead-acid and lithium.

We’ve written an in-depth comparison of lead-acid vs. lithium batteries previously on this blog, but here are the Cliff’s Notes: lithium is the premium option, with a longer lifespan and fewer maintenance requirements. Lead-acid costs much less up front, but regular check-ins are required to keep the battery bank working properly.

Understanding battery types and chemistries can be confusing for those new to solar energy. It’s important to understand the basics of how they are different so you can choose the right battery type for your solar power application. Today we will address the difference in a flooded lead-acid battery and a sealed lead-acid battery.

A flooded battery with lead-acid chemistry is the most common in the industry compared to a sealed lead-acid battery, which are sometimes referred to as a valve regulated battery, an AGM battery (Absorbed Glass Mat) or a gel battery. On paper, there are many similarities between the two battery types. Most of that has to do with their performance, their depth of discharge abilities, their warranty and their cycle life.

The largest difference between the two battery types is the issue of battery maintenance. With a flooded lead acid battery, water needs to be added every so often, periodic equalization needs to be performed and the specific gravity of the electrolyte needs to be measured on occasion with a hydrometer. Another distinguishing factor with a flooded battery is that they can off-gas hydrogen in certain battery charging conditions, resulting in the battery needing to be vented to release the fumes. In stark contrast to the flooded battery, a sealed lead-acid battery requires no maintenance and do not require venting which is a large selling point for those that do not want to deal with battery maintenance. One potential drawback of a sealed lead-acid battery is that due to the inability to maintain the battery, it may not perform at optimum levels as its flooded counterpart.

Aside from the maintenance aspect, the two types of batteries are similar in size, weight, performance and efficiency. There are some minor pros and cons between the two, but the maintenance factor is the largest and most noticeable difference when customers decide on which battery type to purchase.

Flooded lead acid batteries are the most commonly used solar battery. First used for vehicles like golf carts and forklifts, flooded lead acid (FLA) is one of two types of lead acid batteries used in solar power systems.

The other type of lead acid battery is the sealed lead acid battery (SLA). Both batteries have the same size, weight, efficiency and performance.

The key difference between flooded lead acid batteries and other batteries is that they’re the only battery that requires maintenance to keep them working properly.

If you’re new to lead acid, check out my beginner’s guide to lead acid batteries for the basics.

Are flooded lead acid batteries a good solar battery?

Flooded lead acid batteries are the cheapest solar battery. They have the lowest cost per amp-hour and cost per kWh cycle of all deep cycle batteries. The upfront cost is up to 2-3 times less than lithium batteries.

Features of flooded lead acid batteries.Flooded lead acid battery features.

Flooded lead acid is a “wet” battery. This is because the battery’s cells are submerged in distilled water. The water needs to be replaced about once a month as it depletes when you use the battery. Not topping up the water reduces the battery’s lifespan.

The battery also needs an equalizing charge once every three months. This is a controlled overcharge that research shows helps extend the battery life.

An equalizing charge and refilling the water is the key maintenance you need to perform on a flooded lead acid battery.

Another key thing to know about a flooded lead acid battery is gassing. This is a chemical reaction that happens in the battery in which it releases hydrogen as a by-product.

Flooded lead acid batteries must be kept in a well-ventilated area to allow the hydrogen to escape. The hydrogen is potentially explosive in an enclosed area.

Gassing happens about once a month and it’s the reason the water in the battery gets depleted.

If properly cared for and discharged to only half of their capacity, FLA batteries can last from 4 to 8 years.

Check out this guide to sealed lead acid batteries to find out how long they last.

Should you get a flooded lead acid battery?

Flooded lead acid is cheap. This makes it an attractive option if you’re looking to buy solar batteries. But should you choose them over sealed lead acid or a lithium battery? There are certain specific situations where it’s worth it to go with flooded lead acid over the other options. These are:

  1. If you just want battery backup in case of load shedding or blackouts.

  2. For everyday use in an off-grid home.

Pros and Cons of flooded lead acid

To summarize, let’s look at the pros and cons of flooded lead acid.

Advantages of a flooded lead-acid battery

  1. They’re cheaper than lithium.

  2. Longer lifespan than sealed lead acid batteries.

Disadvantages of flooded lead-acid battery

  1. Require maintenance.

  2. It can only be installed upright. Sealed lead acid can be installed on its side which can sometimes take up less space.

  3. Gassing poses another potential safety problem.


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