Ever wonder how renewable energy such as solar, wind, and hydro are stored? A deep-cycle battery that allows consistent discharging and recharging to maintain and optimize its performance, as well as life span, is currently the most recognized and widely-used option to store these energies.
The primary characteristic that distinguishes deep-cycle batteries from other energy storage options is their capacity to undergo a deep discharge before requiring a recharge. Basically, all deep-cycle batteries should have a depth of discharge higher than 80%. Tapping on the worldwide trends and interests in renewable energy, let’s find out how to pick up the right deep-cycle batteries for a more efficient renewable transition.
Introduction to deep-cycle batteries
Types of deep-cycle batteries
- Lead-acid batteries
To better understand the types of deep-cycle batteries available in the market now, let’s first look at each of their development timelines. Flooded lead acid batteries are generally recognized as the oldest type of deep-cycle batteries in history with their foundation dating back to the 1880s. It’s called “flooded” in line with the fully immersed electrolyte beneath its electrodes or plates.
It was followed by the invention of the modern sealed lead acid gel battery in 1934, which is also known as a valve-regulated lead acid (VRLA) battery. It got its “sealed” and “valve regulated” names from the sealed structure and the pressure release valves that keep gas from escaping. Another subcategory of the VRLA battery – the absorbed glass mat (AGM) battery was then officially announced in 1972.
The main differences between a sealed lead acid battery and a flooded lead acid battery, as its name suggests, lie in the “sealed” top covers between them. Sealed batteries are free of the potential leak acid issues in view of their top-sealed design even if they are knocked over or emit gas when being charged. On the other hand, flooded lead acid batteries are not sealed and they always feature removable caps for distilled water refilling.
This is necessary because the gas-to-liquid recombination process does not occur internally in flooded batteries but the gasses are vented outside. As a result, the flooded lead acid batteries require periodic maintenance by refilling the distilled water, which is essential to bring the electrolyte level back to a desired level as gasses generated throughout the charging process are released into the atmosphere.
- Lithium batteries vs lead-acid batteries
In any case, no matter how distinctive the three lead-acid battery subcategories may be, after all, they still fall within the same category as lead-acid batteries. Therefore, the truly subversive qualities of deep-cycle batteries can only be amplified by comparison to the newest type of deep-cycle battery—the lithium battery. Here are some of the main distinctions between them:
- Different electrolytes: The electrolyte of a gel battery is a gel, whereas the electrolyte in lithium batteries is a non-aqueous liquid organic electrolyte. Since non-aqueous solutions use only non-water-based solvents, they have a lesser degree of dissociation and therefore are generally more stable compared to the aqueous solution such as gel electrolyte.
- The working principle: For lithium batteries, lithium ions produced by the positive electrode during the charging process are transported through the electrolyte to the negative electrode. The charging capacity increases as more lithium ions enter the negative electrode. This means a higher charging capacity is made possible by embedding more lithium ions.
- Safety: Different materials used in lithium batteries have varying safety levels. In contrast, gel batteries, as a more mature technology with a long history, provide a greater level of safety than lithium batteries.
- Service life: Lithium iron phosphate batteries have a longer service life which can be charged around 1500 times without experiencing memory effects. It retains roughly 85% of its initial storage capacity after 1500 times. In contrast, the gel battery is only capable of retaining memory up to 500 charges.
- Efficiency and performance: Lead acid batteries with colloidal electrolytes are also called colloidal batteries. They typically have low self-discharge and are therefore conducive to long-term storage. Their high and deep discharge performance helps to improve the deep discharge and over-discharge recovery ability, utilization rate, and discharge capacity of active materials.
- Ecologically friendly: Lithium batteries do not emit any pollutants, whereas colloidal batteries do.
The commercial potential of deep-cycle batteries
When assessing the market potential of deep-cycle batteries, we can look at it from the lens of the prediction of the growth of the market itself, which according to a short-term prediction between 2022 to 2025, should hit US$ 2.41 billion.
On the other hand, since the use of deep-cycle batteries is now closely linked to the growth of renewable energy, it makes sense to gain more insights about the commercial viability of deep-cycle batteries through the perspective of the exponential development of renewable energy, such as solar power and wind energy.
The solar power market, for instance, is expected to grow at a steady compound annual growth rate (CAGR) of 7.2% from 2022 to 2030 and is anticipated to reach an astounding US$ 368.63 billion in 2030. The wind energy market, at the same time, is predicted to expand at an even stronger CAGR of 9.5% up to 2030 and climb from the estimated value of US$ 77.77 billion last year to US$ 174.75 billion in 2030.
Guides to choosing a deep-cycle battery
Deep-cycle batteries come with diverse price tags. Similar to any other product sourcing process, the budget decision should be closely aligned with the target audience and target market. Flooded lead acid batteries, for example, are typically priced around US$ 100 and may be the most economical go-to type of deep-cycle battery for any wholesaler aiming to be the price leader.
AGM batteries, meanwhile, normally come with better offers than their other VRLA counterparts- the gel batteries. AGM batteries with lower capacity can cost around US$ 80-100, whereas those with higher capacity may easily cost more than US$ 500 or more. And of course, lithium batteries, as the newest technology with a much longer life span expectancy usually come with the highest quoted price. In fact, it is common to find lithium battery costs at a low four-digit price level.
Battery capacity, often labeled on specifications as nominal capacity, refers to the measurement of the total energy one can store in a battery, hence naturally extra battery is required to support a bigger load for certain appliances that require extended operation hours. Battery capacity is measured in amp-hours, representing the amount of current that can be sent during a specific period of time.
Yet the specific time frame here is determined by the C-rating, which is the rate at which a battery is charged or discharged. C-rating typically ranges from 0.05C or C/20 (which means 20 hours) to 5C (which means 12 mins). To determine the per hour amps battery capacity of a deep-cycle battery, one simply needs to understand the total battery capacity and divide it with the applicable c-rate as shown in the following calculation examples:
Battery capacity = 100 amp-hours (Ah); Typical c-rate = C/20 (20 hours)
Hence the per-hour battery capacity is 100/20 = 5 Amps capacity over a 20-hour period.
Battery capacity = 100 amp-hours (Ah); Faster c-rate = 5C (12 mins)
Hence the per hour battery capacity is 100/0.2 = 500 Amps capacity over 12 mins!
Fortunately, the internet has enabled a much easier life for anyone who prefers to reserve the standard math chores for computing. As long as you know the battery capacity and the c-rating specification, simply key in the details over an online c-rating calculator and you will get an idea of how much capacity a battery can generate per hour or reversely, how much time the battery needs to be fully discharged.
Depth of discharge and cycle life
Depth of discharge (DoD) is an important specification for the operation of rechargeable batteries. It is usually measured in percentage to indicate the actual usable battery capacity. In other words, the higher the depth of discharge percentage, the longer time a battery can work before the next recharge is required. Although closely related, the total battery capacity measures the total energy available when completely charged, whereas the depth of discharge determines the maximum amount of energy that may be safely used for longer battery life.
The depth of discharge also comes with a direct inversely proportional relationship with the battery cycle life–the total charge and discharge cycles of a battery prior to a decline in performance. This means that a battery will have less cycle life as its depth of discharge percentage and charging frequency increase.
For example, as shown in this research paper diagram here, there is an inversely proportional direct relationship between the cycle life of several types of batteries. Flooded lead acid batteries are reportedly able to achieve around 4300 cycle life at a 50% depth of discharge rate but are around 1000 cycle life lesser shall it be discharged at a 70% depth of discharge rate. The lifespan of a deep-cycle battery clearly gets shorter with each increasing DoD percentage.
Since the cycle life of deep-cycle batteries differs significantly depending on technologies, it is, therefore, useful to understand the recommended depth of discharge per each type of deep-cycle battery. It is, however, important to know the differences between the maximum DoD rate a deep-cycle battery is capable of achieving compared to its recommended DoD rate.
While most deep-cycle batteries may be discharged beyond 50% or even up to 80-100%, they may not be able to last long or perform at their best with an overly high DoD rate. The recommended DoD rate for flooded lead acid batteries for example is 50%, whereas, for AGM and lithium batteries, the recommended rates range from 50% to 75%.
On top of the main spec considerations listed above, a few other factors that people often take into account include the size and weight of the batteries, which are particularly important if they are meant for installation on recreational vehicles (RVs) since there may be space constraints as well as maximum load concerns.
The compatibility issue on the other hand is at its core when it comes to the voltage rating specs. All devices work with a certain fixed voltage and similarly, proportionate voltage rates are required in order to function the appropriate devices. Most RVs operate at 12 volts and correspondingly, the majority of deep-cycle batteries support 12 volts although batteries with 24 volts or 36 volts are not uncommon too.
The durability of a deep-cycle battery is another common concern, which is often reflected in its tolerance over various extreme temperatures, so as to remain stable in its power delivery despite different temperature changes.
Popular deep-cycle battery types
As a deep-cycle battery with the longest history, flooded lead-acid batteries are generally well-received despite their regular maintenance requirement. In fact, they are well recognized as the most commonly used batteries for cars and trucks, and according to experts its distilled water refilling routine, may not be that troubling to automotive owners after all.
The proven reliability and long cycle life in view of their thick antimony alloy grids, compared to the typical calcium alloy grids of VRLA batteries are some of the features that make flooded lead acid batteries popular.
The fact that they have the most economical prices among all the deep-cycle battery types, however, may be the major attraction to most. For example, one can get a wholesale flooded lead acid battery with enough power for forklifts and other small electric vehicles for under US$ 50.
Meanwhile, for flooded lead acid batteries suitable for solar power or wind energy storage, such as the one displayed in the picture below, the prices range between US$ 80 to US$ 100+ for any bulk wholesale orders.
AGM batteries are the most popular type of VRLA batteries due to their cost-effective price level and improved safety advantage compared to gel batteries. Unlike gel deep-cycle batteries with electrolytes suspended in the battery casing by gel paste, the AGM batteries hold their electrolyte entirely in the glass fiber mat, which greatly increased its leak-proof safety feature.
The fact that AGM batteries can support higher capacity and yet come with lower internal resistance is another reason that makes them preferable over other lead-acid batteries, specifically for heavy load applications which require fast charging such as camping and recreational vehicles.
The affordability of AGM batteries is especially evident for those that are suitable for light electric vehicles such as this 75Ah AGM battery which is ideal for an e-bike or another AGM battery with 120Ah capacity which is similar to the one featured in the picture below:
AGM batteries for solar power storage or RVs, on the other hand, typically fetch a higher price tag given their much higher capacity. Some can easily cost more than US$ 250 even at a wholesale bulk order level. However, there are also some smaller capacity AGM batteries for solar energy storage that start from 75Ah and are therefore offered at a much lower wholesale price.
Compared to all other types of deep-cycle batteries, the development of lithium batteries, which officially established their name with the invention of lithium-ion batteries in 1985, is still in its infancy. Nevertheless, as the latest invention among the deep-cycle batteries family, lithium-based batteries are often lauded as the best deep-cycle battery type.
And it is no coincidence that lithium-based batteries are perceived this way. From c-rating to cycle life to depth of discharge and even energy density, which measures how much energy a battery can store given its size or weight, all findings suggest that lithium-based batteries perform better than other deep-cycle batteries. Yet lithium-based batteries are normally problem-free and significantly lighter when it comes to weight and memory effect issues.
Despite its enormously rising popularity, the major downside probably is still its rather higher price, even though it is anticipated to be drastically reduced in the near future. At a bulk wholesale order level, a 12v lithium-ion battery from 100Ah, for example, may still cost around US$ 150 per piece.
At the same time, a single OEM 12v lithium-ion battery with 50Ah may cost at least another US$ 100 extra. A high-end lithium-based battery suitable for storage of solar energy, on the other hand, comes with a minimum starting price of US$ 1500 even with bulk orders. A more balanced approach that a wholesaler may adopt to tackle these diverse cost levels, is to work with a custom lithium-based battery manufacturer to work out tailored, specific voltage for targeted applications.
Embracing green energy storage
The popularity of green energy usage spurred storage needs for them. Deep-cycle batteries are the answer to address these pressing storage needs. Lead-acid batteries and lithium batteries are the two main types of deep-cycle batteries. And their purchase decisions can be based on price, battery capacity, depth of discharge, cycle life, as well as other miscellaneous factors such as voltage, durability, size, and weight. Flooded lead-acid, AGM and lithium-based batteries are the three most popular types of deep-cycle batteries at the moment. Since this is a very broad topic that involves an understanding of multiple technical specifications, it is recommended to read more deep-cycle battery related articles on Alibaba Reads for further details.