Before choosing a battery type, one should know the characteristics of batteries as well as the product requirements. Users will be able to select the appropriate type of battery if they know its internal mechanisms, how it works, its advantages and its limitations. This article will discuss the types and technologies of both disposable and rechargeable batteries.
Some important factors to consider when choosing a battery type:
- Capacity: Battery power must be consistent to meet the expected run time of an application.
- Full charge voltage and end of charge voltage: It determines the number of cells a battery is required for a given application. On the other hand, the use of voltage converters or regulators might be dictated by it.
- Maximum rate of discharge: There is a limit on maximum current that a cell can safely provide, and this is true for all cells. The battery should have an adequate discharging rate to meet the application requirement. If its cells get discharged early, then the number of cells should be increased in the battery pack, or the cell with the higher discharging rates must be selected.
- Temperature range: Temperature has the most significant effect on batteries because many factors are temperature dependent. Cell capacity varies with temperature changes.
- Size and weight: Volumetric (energy density per unit volume) and gravimetric (energy density per unit weight) should be considered when choosing a cell technology.
- Safety: Safety should be the utmost priority when choosing a battery. Sometimes additional protection is required for a specific type of cell for safety concerns.
- Self-discharge: All cells discharge themselves even if a battery is not in use. However, self-discharging time is not the same for all cell types.
- Degradation: Applicable to rechargeable cells only, with every charge/discharge cycle, the capacity of rechargeable batteries degrades permanently.
- Shipping requirements: Some batteries come with strict shipping requirements, specifically for air-shipments.
Technologies and uses of disposable batteries
Disposable batteries are not rechargeable and are wasted after use. They have various coin types and some well-defined sizes, for example, AA, AAA, C and D.
Alkaline, zinc-carbon and lithium batteries
Alkaline, zinc-carbon and lithium batteries are some of the most common types of batteries. They come in cylindrical or button types, and voltage-based types such as 6 V or 9 V. A fresh single cell has a nominal open-circuit voltage of 1.5 V, with 1.65 V being the highest voltage and approximately 0.9 V to 1.0 V as the end of the discharge voltage.
The gravimetric energy density of alkaline cells is about three to five times higher than that of zinc-carbon batteries, which is about 100 to 190 (WHR)/kg. Non-rechargeable lithium batteries are about 200 to 270 (WHR)/kg. The weight of the battery required for a specific task can be roughly estimated using these figures. They can achieve moderate discharge rates but at the cost of reduced capacities.
Zinc-air or silver oxide chemistries are coin-type batteries with the nominal voltages of almost 1.3 V to 1.6 V. Lithium manganese dioxide types are also coin-types with almost 3.0 V. These batteries, other than lithium manganese, come with lower discharge current capabilities. Alternatively, CR2032 (lithium manganese coin cell) can be discharged at 100 mA or even more, and it has a relatively flat discharge curve at low discharge rates.
So, if budget is not an issue, then lithium manganese is the best option for applications requiring coin cells.
Lithium thionyl chloride batteries
A lithium thionyl chloride battery is recommended when an application requires a 15 to 20 year shelf life, high energy density, and can work in conditions from -55° C to 80° C. The only disadvantage is that it has a very low discharge rate. So, to improve its transient response, a large decoupling capacitor is needed. These batteries are costly as well.
For rechargeable batteries, a wide range of choices exist. Because of this, a wide set of issues also exist to consider when choosing the right technology for an application.
Lead acid batteries come with low volumetric and gravimetric energy densities around 60 to 75 Whr/L and 34 to 40 Whr/kg, respectively. As such, they are quite heavy and large for a given amount of energy storage.
Additionally, they have a cell voltage of almost 2.1 V, though they are commonly found as 6 V or 12 V batteries. They also have high self-discharge at 5% to 20%/month. Their low cost and high discharge rate capabilities distinguish these batteries from others. These batteries are also easy to charge and appropriate for automobiles but not for consumer electronics.
Lithium-ion (li-ion) batteries fundamentally store energy in the same way as other batteries. They are the highest energy density technology known so far and are most commonly used for modern electronic products.
Yet, li-ion technology has very strict precautionary measures to ensure safe operation and handling. While using li-ion batteries, safety measures should be considered carefully because they might cause products to catch fire.
These batteries must be mounted inside enclosures with great care. Internal shorts in the core can occur if a device is jerked or dropped, causing the battery to rattle around and incur dents or bruises. Consequently, these can lead to overheating or sometimes explosions.
There must be a protection circuit module (PCM) with a li-ion cell. These two are generally bundled together, which makes it a battery pack. PCM must have the following:
- Under-voltage protection
- Over-voltage protection
- Over-current protection
Choosing the right type of battery requires a lot of background knowledge. Batteries should not be purchased based only on size or shape. All specifications should be read thoroughly to select the appropriate battery.