Environmental >> NiMH Batteries Explained

On this page: introduction | history and types | notes about nimh | how do i convert? | products i've used

 

Introduction

 

If one piece of advice has become valuable in the digital age, it's "buy the right batteries." Besides the fact one person can keep thousands of pounds of solid waste and toxic chemicals out of the landfills if they do the right thing, the cost savings are self-explanatory.

After extensive testing on my own time, I have a lot that I can share with you about this, and I have a feeling that once you start on this path, you won't want to go back.

 

History and battery chemistry types

 

Batteries have a venerable history of their own, and as always, I recommend further reading if you're into the sciences. There's a lot of fascinating and highly useful information out there.

As far as daily living goes, there are two types of batteries (or more correctly, "cells" when referring to singular units) that are commonly available: primary and secondary cells. Primary is disposable, while secondary can be recharged many times. The first portable power solutions to hit the market were primary batteries, beginning with the dry cell. As time went on, the dry cell met with improvements to its chemistry, finally settling on zinc, carbon and manganese dioxide to generate electricity. Later on, as new technologies were invented, the dry cell became deprecated in favour of longer-lasting primaries, namely the alkaline cell, which uses materials suspended in a strong base (usually potassium hydroxide) to generate electricity.

As far as offering easy-to-carry power to the masses, the battery was one of the best inventions of all time, but it came with an unintended cost to the environment. The reign of primary cells for over a hundred years has brought with it manufacturing and end-of-life processes that are are extremely wasteful. Production of a typical primary cell requires approximately one hundred and fifty times the energy contained in the cell once it's reached a marketable form. The disposal of depleted cells not only fills up dump space, but it can leach toxic chemicals into the land and water and tends to be all-around bad news for nature.

During the 1980s a first generation of everyday-use rechargeables, nickel-cadmium cells (NiCd), achieved success on the mass market. Reinforced by TV commercials advertising the attractive cost savings of reusable batteries to customers, many bought them. The unfortunate down sides to this early stage of the technology is that it wasn't mature, and it certainly wasn't practical enough to unseat alkaline as the king of power. A lack of good end-of-life recycling options, poor power capacity, self-discharge issues, and high materials toxicity have dogged NiCd rechargeables for many years. While much of this has changed with continuing improvements to existing technology, they still discharge quickly and tend to maintain a shelf life of about 20-30 days per charge.

But all that has changed. In the late 1990s, a new technology called nickel-metal-hydride (NiMH) hit the shelves. Expensive and scant at first, and unable to deliver more than a few weeks of shelf life between charge cycles, the very first incarnation of this technology was better than NiCd, but still not enough to put alkaline away for good.

From 2000 onward, the further advanced development of NiMH has brought this technology to do a drastic turnaround. After ten further years of work, the technology is finally mature.

Current new-generation NiMH cells (marketed as "pre-charged") now carry a viable shelf life of more than a year between charges, plus they are capable of delivering identical or better performance than alkaline cells in almost every device, providing more consistent voltage and flatter discharge curves. The only device they aren't yet suitable for is the smoke detector, which requires 2+ years of standby power, but I still have a feeling we'll see this barrier broken in the not-so-distant future.

In a parallel universe (of sorts) the advent of portable media devices has spurred the development of two very different types of secondary cell: lithium-ion and lithium-polymer. Able to contain more power than either alkaline or NiMH, they have primarily seen action in the form of specialized batteries built for devices such as iPods and laptop computers. Some of the newer power tools also offer lithium as a battery option. There are, however, no all-purpose lithium cells on the market because these battery chemistries create a different voltage which is unsuitable to any devices using AAA, AA, C, D or 9V. Because lithium runs at 3 or 3.7 volts, requires special circuits to prevent total discharge, and must be maintained within strict charge and temperature guidelines, the only devices properly suited to its application are complex digital electronics. This is unlikely to change any time soon.

 

Interesting notes about NiMH

 

Finding the Right Type

• The only NiMH batteries worth buying are the current generation low self discharge type (LSD NiMH)
• LSD NiMH batteries can usually be distinguished by a white top button seal, and especially if you see words on the package like "holds charge over 1 year" or "pre charged" on the package
• LSD NiMH has a typical power capacity of 2000 to 2600 mAH in AA size, meaning it's a better performer than alkaline
• LSD NiMH does not slowly fade out when it discharges, it tends to hold a relatively constant voltage until it finally runs out of power
• NiMH cells have safety features built in to prevent an explosion or leakag, including vents and use of less volatile chemicals

Life Cycle and Longevity

• Typical NiMH cells are reusable for 1000 cycles when used as directed
• There is no such thing as a "memory effect" in these cells
• Smart chargers can also "top up" cells that have been lightly used

Environmental Benefits

• NiMH technology uses safer materials, reduces solid waste output, and is recyclable (more info here)
• Many high-tech equipment vendors already have contact with a program for recycling batteries

Financial Benefits

• If you were to power a device requiring four AA batteries for a total of 1000 battery life cycles, purchasing a single pack of four NiMH cells costs about $12 and could cover these needs adequately.
• If you tried to do the same thing with alkaline cells, you'd end up buying four thousand cells at a total cost of more than $2500 at current market prices.
• As you can see, it's like night and day. When you begin to look at the numbers and compare technologies side-by-side, the savings and environmental benefits of NiMH become obvious.

 

How do I convert to NiMH?

 

First, you need to make sure your devices will handle NiMH. These cells run at 1.2 volts per cell in contrast to alkaline's 1.5 volts per cell. That's almost meaningless, though, when you consider that most modern electronic devices use microprocessors that can handle a range of voltages without issue. Most of today's electronic gadgets accept rechargeables without complaint, and if you're in doubt, it's still worth a try.

The most effective method of standardizing a battery collection I've found to date is to purchase a supply of AA and AAA cells, some 9V batteries, and several AA-to-C and AA-to-D plastic adapters. Full-fledged C and D cells do exist, but most of the current market offerings aren't good enough to justify the price. If you must have high-capacity C and D cells rated at 5000 mAH or better, you can source them from online vendors like Tenergy.

High capacity NiMHs are also sold cheaply on eBay, but this is something of a gamble. If you buy yours there, I'd advise sticking to well known brands and original packaging, because batteries are one thing where (more often than not) you end up getting exactly what you pay for.

Estimating your needs is simple: the average person needs enough NiMH cells to cover one and a half times the total battery load requirements of their household. This allows family members to easily cycle in fresh cells as existing ones become exhausted and come up for recharging. It also ensures you'll have reasonable reserves in the event of a power failure. To get your estimate, take the total number of batteries needed in all devices within your home and multiply by 1.5.

Chargers should be treated as a one-time quality investment. Look for a smart charger that supports delta-v (voltage change) detection, temperature detection, and other protections. Make sure it is capable of charging single and multiple cells. The reason this is so critical is because many devices on the market make use of odd numbers of cells, and you need a charger that can keep up.

Make sure that the equipment you buy is capable of delivering a fast charge. One to two hours is good, but you shouldn't go any faster than that because it may put too much energy into the cell too quickly, shortening its life cycle. For many customers, this can literally make or break the entire experience. Back when I bought my Sanyo quick-charges, all my power needs seemed to magically sort themselves out right after that. Batteries have since become something I hardly ever think about. I just recharge the occasional set of batteries when needed, pop them back into my gear, and that's that. There's never been a better way of doing it.

Last but not least, invest the thousands of dollars of savings in something worthwhile and give yourself a pat on the back for a job well done.

 

Products I've Used

 

My recommendation is to buy the Sanyo Eneloop charger, as it has these capacities plus it's a one-hour system that plays well with Eneloops and the white President's Choice cells. On that note, the President's Choice kit counts as a quality investment too, but note that while the batteries are high quality Japanese re-brands, the charger is slower than the Sanyo model.