From a very early age we encounter batteries, even if we’re not the ones using them. They’re in the cars we drive, our clocks, phones, watches, computers, and even home alarm systems. In fact, an increasingly large number of electronic and mechanical devices have a battery of some sort. The thing is, because we’ve become so acclimated to them, few people think about what really goes into a battery, or the differences between types of batteries.
The actual science behind batteries is both fascinating and quite complex, but the basics can be explained with relative simplicity. There are essentially two categories of batteries, those that can be recharged and those that can’t. This is important to keep in mind, because fundamentally each operates on same principle, but they are used for very different applications, with each having its own set of advantages and disadvantages.
The basic principle on which all batteries operate is the conversion of chemical energy into electrical energy. In principle this is no different than your body converting food into energy, or your car converting fuel into energy. The process involves converting one thing into something else. In the case of batteries, how that conversion takes place is what makes the difference between rechargeable and non-rechargeable batteries.
Non-rechargeable batteries are also known as primary cells. They’re typically what you see advertised on TV, or will use in a flashlight or child’s toy. They’re also common in standalone smoke detectors, wrist watches, and calculators. You can’t recharge them because they consume the catalyst for the chemical reaction when they generate electricity.
Rechargeable batteries are known as secondary cells. While they are also available in sizes like you would use in a child’s toy or flashlight, they’re more commonly seen as car batteries, in cell phones and laptops and the like. These batteries can be recharged because the catalyst is not consumed. Instead, it changes state depending on whether it is charging or discharging. There are still limits to how often and how long these batteries can be recharged, which can vary from one type of battery to the next.
Within these two categories there are several different types of battery cells. However, the two most common are the dry cell, and the wet cell.
Wet cell batteries, as the name implies, involve a liquid electrolyte. The most common type of wet cell is a lead-acid battery. They are the oldest type of battery in use, make up more than 40% of the batteries sold worldwide, and are a $15 billion industry in the U.S. Current is produced when ions move from the lead and lead oxide electrodes, facilitated by the chemical reaction of the acid electrolyte. When fully discharged the battery is mostly just lead plates and water, with the acid having chemically reacted with the lead plates. If current is reintroduced to the battery, the cycle is reversed, with the electrolyte solution of water and acid becoming more acidic as the battery is recharged. When the battery will no longer hold a charge, the lead plates will be very corroded by the acid, and the electrolyte solution will be almost entirely water.
Most lead-acid batteries need to remain upright due to the liquid electrolyte, and they produce a small amount of gas as the liquid acid electrolyte is depleted. This type of battery is most commonly found in automobiles, and requires occasional maintenance. Some, however, are sealed, and do not need to be kept upright. These sealed wet cells are considered maintenance free, and have special applications, most commonly as either an alarm battery or an uninterrupted power supply (UPS) battery for computers.
Conversely, dry cell batteries do not need to be kept upright, and as a result are more portable. Because of this they are found across a much wider range of applications. In fact, chances are you’re using a dry cell for just about everything except your car. The two most common types of dry cell batteries are alkaline and lithium-ion.
Alkaline batteries are likely in your flashlight, cordless phone, and portable radio. They generate electricity when the zinc powder of the negative terminal interacts with the manganese dioxide of the positive terminal. The catalyst for this reaction is the alkaline electrolyte potassium hydroxide, which is consumed on discharge. Once the catalyst is used up, the battery will no longer produce a charge. There are rechargeable alkaline batteries available, but they’re uncommon.
Lithium-ion batteries, which are in cell phones and laptops, are more complex and varied. Basically they produce current when positively charged ions move from the negative graphite battery terminal to the positive lithium terminal. When the battery is recharged, the current forces the ions back to the negative terminal, allowing the process to repeat itself. The catalyst is cobalt, which is oxidized as the ions move to one side or the other. When it is gone, the battery will no longer hold a charge.
Now that you have a better idea of the different battery types and chemicals that make them work, it is time to consider the important factors relating to power. These are the capacity and discharge rates, and the total battery lifetime.
Capacity and discharge measure how much charge the battery can potentially hold, and how that charge is dissipated. Standard ratings are measured over a period of 20 hours, at room temperature. For example, a 100 A-h rated battery will discharge at the rate of 5 amps per hour. There are also very rare and expensive high-capacity, short-duration batteries. The most expensive battery in the world is in China, and valued at $500,000.
Battery lifetime is another consideration, and one that changes with the temperature. The lower the temperature, the less battery power one will have. Additionally, for rechargeable batteries, the more times they are discharged and recharged, the less overall capacity they will have. This is because they build up internal corrosion, until they reach a point where they no longer function. It also means that battery lifetimes are always estimates, especially for rechargeable batteries, as so many factors can impact the actual performance.
So, what is the best battery?
Well, there isn’t one all-purpose battery that can do everything. In most cases you’ve got a lemon on your hands unless you’re using the correct battery for the equipment you want to power. Batteries have not kept pace with advances in consumer electronics, forcing manufacturers to create different types of batteries for different applications. This is why a cell phone, a house phone, and a police radio might all have very different batteries with different charge capacities and lifespans, despite fairly similar uses.
Because of this, and the relatively low cost of quality batteries, it is best to follow manufacturer instructions over inaccurate myths, such as storing batteries in the refrigerator (which can potentially damage them). If you need a new battery, see what the manufacturer of your product recommends, and buy what they recommend. Whatever you do, don’t play with trying to charge batteries that weren’t mean to be recharged. They can explode and cause serious injury.
If you insist on playing with batteries, pick something safe, like a battery that is really a lemon. Seriously, try it, or let your kids try it and learn something new.