These days just about everything we use needs batteries, and while they’ve become indispensable to us in our technological age, very few of us understand how they work, or what the difference between lithium-ion, alkaline, and nickel-metal-hydride is—let alone amp-hours or volts.
With this in mind, we’ve put together a quick tutorial to help you understand this ubiquitous tool and why it’s important to match up the right battery with your device. For the sake of our sanity and to avoid confusion, we’re staying focused on common batteries that power things like flashlights, remote controls, and other such devices.
Anatomy
Terminals Despite the differences in size and shape, the basic anatomy of a battery is the same. First are the terminals, marked Positive (+) and Negative (-). When connected to a load, the stored electrons (the charge) flow from the negative terminal to the positive. A load can be anything from an LED, a light bulb, a motor, or radio. It’s this flow of electrons that powers the device to which the battery is connected.
Electrodes Inside the battery case are two complementary components, the Cathode (+) and the Anode (-), and together they are called Electrodes. The Electrodes take up the bulk of the battery and it’s where the chemical reaction occurs that produces the electrical current.
Separator A barrier separates the cathode and anode so they don’t touch, while allowing the charge to flow between the two.
Electrolyte An electrolyte is the catalyst that allows ions (positively or negatively charged atoms) to move between the cathode and anode. In the batteries we’re discussing here, electrolytes are made of soluble salts, acids, or other bases in liquid, gelled, and dried forms.
Collector The Collector conducts the charge out to the terminals and into (and through) the load.
Power
This is probably the least understood aspect of batteries, and could support an article all on its own, so we’re going to stick to the basics and keep this at primer level instead of delving deep.
There are two terms used to describe the power of a battery: voltage and current. Voltage (measured in Volts or “V”) is the measurement of the difference in charge between the cathode and anode. Current (milliamps for batteries, or “mA”) is the rate at which the voltage flows. Think of it in the context of this analogy: if the battery charge is water, then voltage is pressure and the flow of the water is the current. Another term that is often seen with batteries is Amp-hour (“Ah” or “mAh”). Staying with the above analogy, the battery can be considered as a tank holding the water (power), so the amp-hour is the capacity of the battery. 1 mAh is the amount of charge transferred by moving 1 mA over one hour.
In relation to batteries and mobile electronics, the way multiple batteries are connected affects both voltage and current. There are two ways to wire batteries together: in series or parallel. When wired in series, (positive terminal to negative terminal) the voltage is cumulative of the number of batteries wired, so if a standard AA battery is 1.5V, then wiring two in a serial circuit will produce 3V, with the capacity remaining the same, at about 2850 mAh. Wiring the same two batteries in parallel (positive to positive/negative to negative) keeps the voltage the same at 1.5V, but doubles the milliamps and mAh.
Why is this important to know? Certain devices, like some of the powerful LED flashlights currently on the market, or vapers/e-cigarettes, require high-capacity rechargeable batteries to function properly. The common size for these are 18650 (more on sizes later), but you can get that size in different capacities like 2600mAh, 3400mAh, or 3500mAh, to name a few.
What this means from a practical standpoint is that if you put a low-capacity battery in a device that requires high-capacity, the device will be pulling the current out of the battery faster than it can safely give and you risk over-heating or over-discharging the battery, which can damage its ability to take and hold a charge. Conversely, if you take a high-capacity battery and put it in a device rated for low capacity, the battery will be pushing the current faster than the device can handle it and you risk damage to the device.
Some devices don’t have a rating, but where it’s important, the manufacturer will tell you which batteries it requires for proper and safe operation.
Chemistry
Disposable While battery chemistries vary, the basic process is the same: a series of chemical reactions between the anode, cathode, and electrolyte. The anode undergoes an oxidation reaction in which ions from the electrolyte combine with the anode, which releases electrons. Simultaneously, the cathode experiences a reduction reaction, which makes it electron-deficient. The electrons from the anode flow through the load to the cathode, which absorbs them. This is essentially electricity—the flow of electrons. The battery will continue to work until either the anode can no longer produce electrons or the cathode can no longer absorb them.
• Zinc-carbon chemistry is common in many ubiquitous AAA, AA, C, and D dry cell batteries. The anode is zinc, the cathode is manganese-dioxide, and the electrolyte is ammonium chloride or zinc chloride.
• Alkaline is also common in AA, C, and D dry cell batteries, but generally in higher-quality ones. The cathode is composed of a manganese-dioxide mixture, while the anode is a zinc powder. It gets its name from the potassium hydroxide electrolyte, which is an alkaline substance.
Rechargeable batteries work similarly to the disposable kind, except the reaction as described above is one-way in a disposable, but the process is reversible in a rechargeable battery. When plugged in for recharging, the negative-to-positive flow of electrons is reversed and the battery is ready again.
Lithium-ion batteries are the most common reusable kind, and are often employed to power high-performance devices, such as cell phones, digital cameras, and even electric cars, and are used primarily where high-energy density and weight conservation is of prime importance. A variety of substances are used in lithium batteries, but a common combination is a lithium-cobalt-oxide cathode and a carbon anode.
Other types of rechargeable chemistries are:
• Nickel cadmium (NiCd) is used where long life, high discharge rate, and economical price are important. Main applications are two-way radios, biomedical equipment, professional video cameras and power tools.
• Nickel metal hydride (NiMH) has a higher energy density compared to the NiCd, at the expense of reduced cycle life. NiMH contains no toxic metals, unlike the NiCd.
• Lithium ion polymer (Li-ion polymer) offers the attributes of the Li-ion in ultra-slim geometry and simplified packaging.
SAFETY NOTE: Check the specification and owner’s manual before swapping disposable with rechargeable batteries in any device. Quite often, there won’t be a problem, but as I mentioned regarding capacities, you need to make sure your device is compatible with the battery type you’re using so you don’t damage the device or shorten the battery life. And whatever you do, DON’T MIX DISPOSABLE WITH RECHARGEABLE AT THE SAME TIME.
Rechargeable Technology
With electronics and circuit boards getting smaller and cheaper while also becoming more intelligent, manufacturers are able to pack a lot of tech into their batteries to help protect them from abuse and lengthen their lives. Many rechargeables now feature integrated electronics that protect against over-charge, over-discharge, reverse-polarity (putting the battery in backwards), and over-heating. These boards monitor the battery and shut off the current if a problem occurs. Similarly, many chargers for the batteries have complementary technologies that cut the charging circuit when the battery reaches capacity to prevent over-charging, and if they sit in the charger for long periods, will send in a maintenance charge (called a trickle charge) to keep the battery full without damaging it.
Final Thoughts
As you can see, there’s more to that little cylinder than meets the eye. Armed with a little knowledge and the key differences to what the confusing numbers all mean, you can now go forth and buy with confidence that you’ll be able to match the right battery with the right device.
Feel free to post questions in the Comments section, below.
