Battery types review 2020

This article will answer the following questions:

• What is a battery?
• What are the most important specs of a battery?
• What are the most common battery types?
• Which parameters affect a battery’s lifespan?
• Which parameters affect a battery’s capacity?
• What is the best type of battery?

What is a battery?

A standard battery consists of two electrodes (an anode and a cathode) and an electrolyte. The anode is negatively charged and the cathode is positively charged. As for the electrolyte, it varies according to the type of battery and has the function of circulating ions from one electrode to another. The ions allow the circulation of electrons inside the electrolyte, the latter being responsible for the generation of an electric current.

That said, when an electrical voltage is applied across the electrodes, an electrical current builds up and creates chemical reactions on the surface of the electrodes and in the electrolyte. During the discharge, the positive plates consume electrons (reduction reaction) and the negative plates release electrons (oxidation reaction). In contrast, during charging, the positive plates release electrons (oxidation reaction) and the negative plates consume electrons (reduction reaction). The product of the electrons exchanges is the generation of an electric current.

What are the most important specs of a battery?

Knowing how to recognize the different technical characteristics of a battery is very useful when the time comes to design a renewable energy production system. Apart from dimensions and weight, the most useful technical characteristics to know are:

• The voltage
• The capacity
• The cyclability
• The maximum suggested depth of discharge

Voltage is the difference in potential between the two electrodes of the battery, which is the equivalent to the strength of the electric current. The most frequent voltages are 6V, 12V, 24V and 48V. Knowing that the product of voltage by amperage is power (Voltage * Amperage = Power), the higher the voltage of a battery, the lower the amperage it must provide to deliver a given power. This implies that the electrolyte of a higher voltage battery will be less stressed during its discharge (due to a lower amperage) which means that it will have a longer lifespan. The acquisition of higher voltage batteries is therefore suggested, although their purchase cost is higher than that of lower voltage batteries.

Capacity is the amount of energy that can be stored by the battery. It is expressed in ampere-hours (Ah) and depends on the intrinsic characteristics of the materials it contains. It generally ranges from 50 to 1500 Ah per battery, although hundreds of different models exist. The higher the battery capacity, the greater the energy autonomy it provides. In the same logic as for voltage, the acquisition of larger capacity batteries is suggested, although their purchase cost is higher than that of lower capacity batteries.

Cyclability is defined as the amount of charge/discharge cycles that the battery can withstand, one cycle being the full charge and discharge of the device. This information is provided by the manufacturer and is generally presented in the form of a warranty. The higher the cyclability, the longer the life of a battery. For example, assuming that a charge/discharge cycle is performed daily, a battery guaranteed for 500 cycles has a lifespan of approximately 1.37 years (500 cycles ÷ 365 cycles / year = 1.37 years).

The maximum discharge depth suggested refers to the ratio of the amount of energy discharged to the amount of energy remaining in the battery. A 75% depth of discharge means that 75% of the battery energy has been drawn and that 25% is still available. For most battery types, a too deep depth of discharge (> 75%) is not recommended since it accelerates the degradation process of the electrolyte. It is therefore necessary to look at the maximum discharge depth recommended by the manufacturer to know how much energy is available per battery.

What are the most common battery types?

Although a multitude of battery types are being tested today, the most common battery types in North America are Lead-Acid batteries, AGM batteries, Gel batteries and Lithium-Ion batteries. Each of these types will be explained and compared to each other.

Lead-acid batteries

Lead-acid batteries are batteries whose electrodes are made of lead and whose electrolyte is composed of sulfuric acid and water (35% sulfuric acid and 65% water). This type of technology is most common in the industry as it is the most economical option.

Pros:

• Their capacity is enough for most energy applications.

• They are reliable (given their technological maturity).

• They are the most economical option.

• They are 98% recyclable.

• They have no memory effect.

Cons :

•They have a low energy density compared to other types of batteries. This implies that for the same capacity, the weight and volume of a lead-acid battery will be much higher than that of another type of battery. They are therefore not recommended for applications where space and / or weight are limiting factors.

• The fact that the battery is not sealed makes the electrolyte more fragile in the face of extreme temperatures. The latter can evaporate when it is too hot or freeze when it is too cold. In both cases, the electrolyte degrades and becomes less effective.

• They are fragile when faced with high charge / discharge intensities.

AGM batteries (Absorbed Glass Mat batteries)

AGM batteries are Lead-acid batteries that are sealed and where the electrolyte is absorbed in fiberglass. The choice of this absorption is explained by two facts. First, fiberglass is an ultra-absorbent material that creates a spill and acid leakproof battery when flipped sideways (unlike Lead-acid batteries). Thus, AGM batteries do not require any maintenance when they have been moved. Second, fiberglass provides lower electrical resistance, which promotes the flow of current between the battery electrodes and results in more efficient electrical transfer.
Improved efficiency means more energy is available per battery.

Pros (facing lead-acid batteries):

•They are less affected by extreme temperatures.

•They have better efficiency.

•They require no maintenance.

• Their recharge speed is five times higher.

• They better tolerate the high charge/discharge currents intensities.

• They have no memory effect.

Cons (facing lead-acid batteries):

• They have a shorter lifespan than lead-acid batteries.

• They are more fragile in the face of overload and deep discharge.

• They are more costly. 

Gel batteries

Gel batteries (also called silicone batteries) look like AGM batteries, the only difference being that silica has been added to the electrolyte so that it is in the form of a viscous gel rather than a liquid. The performance of gel batteries is quite like that of AGM batteries. It is up to the consumer to choose what they prefer between AGM or Gel batteries.

Pros:

• They are even less affected by extreme temperatures than AGM batteries (especially by hot temperatures).

• They have better efficiency than AGM batteries when the intensities of the charge/discharge currents are low.

• They can tolerate great depths of discharge (up to 80%).

• They require no maintenance.

• They have no memory effect.

 Cons:  

• They are more expensive than AGM batteries.

• Their lifespan is still shorter than that of lead-acid batteries (except in very hot temperatures).

• They are more fragile when faced with high charge/discharge current intensities.

• They must absolutely be recharged by a charger made for gel batteries otherwise the electrolyte will degrade very quickly, and the battery must be replaced.

Lithium-Ion batteries

Unlike the three battery technologies explained above, lithium-ion batteries do not have a single combination of elements. Indeed, some combinations of elements are better for supporting high discharge current intensities (LiFePO4) while other combinations have promising capacities (Ni-Li). However, several combinations are still being tested in the laboratory and will not be on the market for several years. The most common combination is LiCoO2, where the anode is made of graphite, the cathode is made of cobalt oxide and the electrolyte is made of metal ions.

Lithium-ion batteries are becoming more and more popular as they offer the highest capacity and the greatest resistance to deep discharge.

Pros:

• They have a much higher energy density than all other types of batteries.

• They are the most resistant to great depths of discharge (can tolerate up to 100% discharge).

• They are the most resistant to high charge/discharge intensities.

• They have the lowest percentage of self-discharge.

• They have no memory effect.

• Their lifespan is the longest of all types of batteries.

Cons:

• They are the most expensive battery technology of all types of batteries (due to the many advantages it provides as well as the novelty of the technology).

• The fact that the technology is immature now means that lithium-ion batteries sometimes do not have constant performance over their entire lifespan

• They are more difficult to access due to their low popularity due to their very high cost.

• Their structure is not as robust as that of the three other types of batteries described above.

Which parameters affect a battery’s lifespan?

Aside from their high cost, one of the main shortcomings of batteries is their short lifespan. Even under the best possible conditions, the maximum lifespan of a battery is around 5 years, although the average warranty never exceeds 2 years. This is caused by the gradual degradation of the electrolyte over time, which will eventually reach a stage of irreversibility.

That said, several factors can also shorten the life of a battery. Being able to understand these factors is therefore essential for anyone wishing to optimize the life of their batteries. These factors are:

• The temperature of the storage location

• The depth of average discharges

The temperature of the storage location refers to the temperature of the location where the batteries are stored. The storage temperature recommended by any manufacturer is 25°C (77 ° F), regardless of the type of battery. Too cold (<0 ° C) will cause the electrolyte to freeze while too hot (> 30 ° C) will cause accelerated degradation of the electrolyte. The figure below shows the effect of warm temperatures on the life of a standard lead-acid battery. It should be noted that this trend is also observable for cold temperatures and for any type of battery.

Which parameters affect a battery’s capacity?

In the same logic as for the previous section, several factors can decrease the capacity of a battery. These factors are:

• The temperature of the storage location

• The intensity of the charge / discharge currents

Again, the temperature of the storage location refers to the temperature of the location where the batteries are stored. The figure below shows the effect of temperature on the capacity of a battery. The higher the temperature, the greater the useful energy available per battery.

However, it should be remembered that high temperatures shorten the life of the battery. So even if the battery capacity increases with temperature, it is still unwise to store it in a place where the temperature is above 25 ° C.

The intensity of the charge/discharge currents refers to the amperage of the charge / discharge currents. Explained by the Peukert effect, the capacity of a battery decreases exponentially when the intensity of the discharge current increases linearly. Knowing that the intensity of the induced discharge current increases the higher the power of a device, the capacity of a battery therefore depends on the power of the devices which it supplies. This means that if you do not want to drain the energy in your batteries too quickly, you will have to be careful with the number of devices that you decide to operate at the same time. The figure below shows the discharge speed of a lead-acid battery (x-axis) in the face of an increase in the intensity of its discharge current (y-axis). Again, this phenomenon is applicable for any type of battery.

What is the best battery type?

We suggest opting for the acquisition of lithium-ion batteries to those who have the means since they offer the greatest capacity, the greatest resistance to deep discharges as well as the greatest resistance to high charge/discharge currents intensities. In addition, in cases where space and weight are limiting factors, lithium-ion batteries are the best solution. We are however aware that this technology is unaffordable and that another type of battery might as well do the trick.

For those wishing to have a maintenance-free system, AGM batteries seem to be the best choice. They are more expensive than lead-acid batteries but have greater resistance to extreme temperatures as well as high charge/discharge current intensities. Gel batteries are also recommended for applications where the average amperage is low and where the ambient temperature is often very high (> 30 ° C).

Finally, lead-acid batteries remain the most economical and reliable choice given the maturity of the technology. For those who first want to explore the world of batteries without having to spend several thousand dollars, lead-acid batteries are an excellent choice.

Do not hesitate to contact us for more information on the different types of batteries, we will be more than happy to help you!

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