The 10 Best NiMH Chargers
Editor's Notes
December 10, 2020:
While there hasn't been a whole lot of technological advancement around common battery formats in the last few years, it's always important to have a safe and effective charger, and in many cases, a full-featured one can make a big difference. For example, our top choice, the Opus BT C3100, is one of the few that's also designed for lithium-ion batteries, and it as well as the La Crosse Technology BC1000 Alpha and Powerex MH-C9000PRO offer advanced features like refresh modes to ensure batteries don't develop a memory. All three of these have been known to be used by professional electricians, and all of our selections are made with premium circuitry.
That includes the Ansmann Energy 4 and Ansmann Energy 16 Plus, both of which even offer the ability to charge 9-volt batteries, and the Panasonic Eneloop BQ-CC55, which works quickly and reliable and is especially easy to use. The EBL C9008 and EBL 6201, meanwhile, are highly affordable and designed for portability, although they don't come with power adapters. You'll have to supply your own for both, and it will have to have a 2-amp output.
Also please keep in mind that none of these are explicitly designed by the manufacturer to charge lithium-ion phosphate batteries or "rechargeable alkaline" batteries.
December 08, 2019:
Nickel metal hydride is one of the most popular types of rechargeable battery because of its capacity, moderate heat output, and minimal memory. There are plenty of chargers to choose from, and they vary a surprising amount in their functionality and reliability. The La Crosse Technology BC1000 Alpha, Powerex WizardOne, and Opus BT C3100 are all quite technologically advanced, offering charge and discharge modes which can be customized to relatively specific amperage levels, helping to extend the life of your cells.
If you use a lot of 9-volt batteries, though, your best bet will be either the Ansmann Energy 4 or Ansmann Energy 16 Plus. The smaller one can accommodate 4 cylindrical batteries or two 9-volts at once, while the larger one can handle 12 AA or AAs, or 6 Cs or Ds (or other wide cells), in addition to its dual dedicated 9-volt slots.
There are a few more relatively simple yet quite reliable options, though they're also limited to AA and AAA batteries. The Panasonic Eneloop BQ-CC55 comes out on top in the speed category but it doesn't have much in the way of readouts and doesn't let you control charging rates. The EBL 6201 is useful for travelers because you can plug it into a power bank if you don't have access to a wall outlet. Similarly, the Superex RPC-C20BK Smart Universal includes a 12-volt adapter perfect for use in vehicles. The Xtar VC4 and Ansmann Powerline 4 Light are both reasonably priced, relatively affordable, and provide more information about what's going on than the simplest options do.
Over 200 Years Of Battery Life
A chemical battery acts much the same, except it uses electrons in place of a round ball, and an electrolyte solution instead of a hill.
In the mid-1700s, US founding father Benjamin Franklin combined layers of glass and metal to form a set of capacitors that enabled his earliest experiments. Breaking from the era's apparent tradition of naming everything after oneself, he called his contraption a battery, because, like a naval battery, it consisted of many parts working together as one unit.
While they may seem complicated or even magical, batteries are just another way to store energy, not unlike a ball resting at the top of a hill. That ball contains a certain amount of potential energy, which we can calclulate based on the grade and height of the incline. A chemical battery acts much the same, except it uses electrons in place of a round ball, and an electrolyte solution instead of a hill.
Of course, when Luigi Galvani first manipulated electricity by means of a dead frog, he didn't know any of that — he attributed the spark to the dubious and since-disproven concept of animal electricity. Luckily, his friend and colleague, Alessandro Volta, was there to set him straight. Obviously, he claimed, this phenomenon came simply from two different types of metal (Galvani's scalpel and working clamps) coming into contact via a moist intermediary (Galvani's unfortunate, amphibious test subject). Volta called this the theory of contact tension, and it is also absolutely incorrect.
Although Volta's reasoning was off, his results told a different story. In the year 1800, he stacked up a series of zinc and copper discs, separating each with a layer of saltwater-soaked cardboard. In a return to familiar naming conventions, this became not-so-eloquently known as the voltaic pile, and many historians consider it the first real chemical battery.
Nearly Endless Potential (Energy)
Many people change a pair of AA batteries without thinking about how they work. And while it's easy to imagine a battery as a fuel tank, but for electronic devices, it's not that simple. Electric charge isn't a physical collection of molecules like water or oxygen; the term specifically describes the presence of free electrons in a system. An everyday battery cell consists of two half-cells, filled with an electrolyte solution, and a positive or negative electrode in either side.
Just like a ball wants to roll down a hill due to gravity, these electrons want very badly to move to the cathode, as they're attracted to its positive charge.
When fully charged, nearly all of the cell's free electrons are on the anode's side, which also possesses a negative charge, based on its chemical makeup. Just like a ball wants to roll down a hill due to gravity, these electrons want very badly to move to the cathode, as they're attracted to its positive charge. The layer separating the two half-cells, however, is a mostly one-way gate. So when the circuit is complete, i.e. the anode is externally connected to the cathode, electrons are pulled from the very tip of that connection into the positively charged electrode, and the remaining negative ions stored in the anode-side solution begin to shed their extra electrons, which begin to flow through the circuit, turning the stored chemical potential into electrical energy.
Scientists arrived at this basic tenet of electrochemical theory when they observed the corrosion of Volta's electrolyte as well as local, electrical inconsistencies around impurities within the solution. The fluid that bubbled and leaked, they proposed, was the result of forcing current through compounds that didn't share exceptionally stable bonds, a process now known as electrolysis.
It was this understanding that enabled European researchers to charge forth from Volta's early work, to the development of unsealed, dangerous, wet-cell batteries, later advancing to fully enclosed, dry cells as technology allowed. In 1859, Gaston Plante gave the world the lead-acid battery when he inserted lead electrodes into a solution of oxygen in sulfuric acid. Various configurations of lead, manganese, ammonia, and numerous other fun substances contributed to continually increased efficiency over the next 100 years. By the middle of the 20th century, chemical engineers finally nailed a new recipe for efficient, rechargeable storage with a nickel-cadmium composition. As devices called for more power, and cadmium mining became expensive and rife with pollution, nickel-metal hydride cells came to the rescue.
Small Packages With Lots Of Power
There's a nearly endless overall selection of battery sizes, shapes, capacities, and voltages. They come as small as the ones found inside watches, and as large as those found in power plants. When it comes to oft-swapped, interchangeable cells, though, a few formats stand above the rest.
Less popular than before, but still relevant, are the C and D sizes.
The two most popular among most devices are the AA and AAA sizes, with which most people are familiar. Less popular than before, but still relevant, are the C and D sizes. All of these output 1.5 volts; the difference among them is the amount of charge stored, as more volume means a larger electrolytic swimming pool for the eager anions. Additionally, 9-volt batteries are particularly popular among mobile radio devicies such as walkie-talkies and wireless microphone systems, which tend to require more oomph than the smaller, cylindrical cells can provide.
And while it's a simple concept that reversing the charge causes the electrons to flow in reverse, doing so practically can pose challenges. Too much current can cause the intermediate substance (usually potassium hydroxide) to break down, which expels gas, causes excess pressure, and releases impurities into the solution. Incidentally, this is also a common side effect of attempts to recharge primary, non-rechargeable batteries. Despite some units' claims that they're designed to recharge single-use cells, many experts explicitly recommend against doing so.
You'll find a number of useful features on different chargers, some of which will help everyday users, and some of which are meant for more advanced tasks. A quality model can detect a battery's overall health in addition to its current charge, and most can fully discharge cells before refilling them. This prevents them from building up any type of memory, which is one of the main points of concern around NiMH batteries. But with the right charger, a moderate understanding of electricity, and a bit of attention to detail, anyone can be on the path to responsible, portable power. Because listening to music on the move and minimizing chemical waste are both pretty good ideas.