Rechargeable Batteries
With the rise in portable devices such as laptops, cell phones, MP3 players and cordless power tools, the need for rechargeable batteries has grown substantially in recent years. The concept of the rechargeable battery has been in agenda since 1859, when French physicist Gaston Plante invented the lead acid cell, which would later become the world's first rechargeable battery.
The basic idea behind the rechargeable battery is simple: when electrical energy is applied to the battery, the electron flow from negative to positive that occurs during discharge is reversed and power is restored. This requires an adapter in the case of devices with built-in batteries or for standard nickel-cadmium or nickel-metal hydride batteries, the most common multi-use rechargeable batteries used today in your flashlight battery or digital camera.
In electric and hybrid cars, traction batteries are used to power the vehicle down the road. Traction batteries come in many varieties, from lead acid, to nickel-cadmium, nickel metal hydride and lithium ion.
The recharging rate has improved substantially over the years and is broken down into three categories:
- Slow: 14-16 hours
- Quick: 3-6 hours
- Fast: Less than one hour
The rate of charge is determined by how much electrical current is allowed into the rechargable battery by the charger. Some batteries can handle higher voltage in a shorter amount of time without overheating, while others need a lesser voltage applied over a longer period of time. The quicker the rate of charge, the more chance there is of over charging, which can ruin a battery's chance of holding its charge. The key in avoiding an over charge is the ability to dissipate the charging current once maximum power has been reached. Most chargers have built-in voltage regulators do this, allowing you to safely leave your cell phone or computer plugged in overnight.
The speed and effectiveness of the charge depends largely on the quality of the charger itself. Chargers vary in performance based on the price tag and like most products you get what you pay for. Chargers are generally designed for specific cell chemistries, although newer universal chargers have sensors built in that identify the cell type and react appropriately. There are also smart chargers that use a microprocessor to monitor temperature, voltage and state of charge, which is the percentage of power available compared to its full capacity.
One common problem in nickel-cadmium rechargeable batteries is something known as the memory effect. This is when the battery is continually recharged before it has discharged more than 50 percent of its power, causing it to essentially forget that it could fully discharge to begin with. Memory effect is caused by the formation of hard-to-dissolve cadmium crystals deep within the battery. Cadmium crystals are an unavoidable by-product of discharge; the trick is to keep them small enough to be reformed as cadmium during the charging process. When a battery is not fully discharged, the crystals deep within the battery are not affected by the influx of electrical current, so they are not reformed as cadmium and can grow into the troublesome larger cadmium crystals. The battery will still function normally, but is maxed out at 50 percent. The memory effect can be avoided by fully cycling the battery once every two to three weeks by allowing it to discharge completely, and then fully recharge.
It's important to remember that no battery, rechargeable or otherwise, will last forever. All batteries suffer from aging cells and the longer they are used, the less capacity they ultimately will have. Rechargeable batteries are still a great way to save money and reduce waste.
Battery Arrangement and power:
In many devices that use batteries - such as flashlights, you do not use just one cell at a time. You normally group them together serially to form higher voltages, or in parallel to form higher currents. In a serial arrangement, the voltages add up. In a parallel arrangement, the currents add up.
In the arrangement called a parallel arrangement if you assume that each cell produces 1.5 volts, then four batteries in parallel will also produce 1.5 volts, but the current supplied will be four times that of a single cell. and in the arrangement called a serial arrangement the four voltages add together to produce 6 volts.
Normally, when you buy a pack of batteries, the package will tell you the voltage and current rating. For example, a digital camera might use four nickel-cadmium batteries that are rated at 1.25 volts and 500 milliamp-hours for each cell. The milliamp-hour rating means, theoretically, that the cell can produce 500 milliamps for one hour. You can slice and dice the milliamp-hour rating in lots of different ways. A 500 milliamp-hour battery could produce 5 milliamps for 100 hours, or 10 milliamps for 50 hours, or 25 milliamps for 20 hours, or (theoretically) 500 milliamps for 1 hour, or even 1,000 milliamps for 30 minutes.
However, batteries are not quite that linear. For one thing, all batteries have a maximum current they can produce -- a 500 milliamp-hour battery cannot produce 30,000 milliamps for 1 second, because there is no way for the battery's chemical reactions to happen that quickly. And at higher current levels, batteries can produce a lot of heat, which wastes some of their power. Also, many battery chemistries have longer- or shorter-than-expected lives at very low current levels. But milliamp-hour ratings are somewhat linear over a normal range of use. Using the amp-hour rating, you can roughly estimate how long the battery will last under a given load.
If you arrange four of these 1.25-volt, 500 milliamp-hour batteries in a serial arrangement, you get 5 volts (1.25 x 4) at 500 milliamp-hours. If you arrange them in parallel, you get 1.25 volts at 2,000 (500 x 4) milliamp-hours.
Batteries have proven to be one of the most important inventions of the 20th century and are becoming more so as we continue the shift toward a more mobile lifestyle. In the future, batteries will grow smaller, more powerful and longer lasting in order to keep up with our fast paced, portable world.
[AA/AAA Rechargeable Batteries]
