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How to Take Advantage of NiMH Batteries

Cordless electric devices are everywhere, and the only reason that's become possible is through developments in battery technology. While you can use disposable batteries for a number of uses, in most cases rechargeable batteries are not only more practical but they are also better for the environment.

What Does Rechargeable Mean for Batteries?

Batteries can divide into two basic categories; there are primary cells, which carry a charge due to their construction, and secondary cells, which you can recharge and use over and over again. A rechargeable battery commonly uses one of four basic chemistries:

  • Lead-Acid: Mostly restricted to larger applications such as automobiles and backup power systems, these were the first common rechargeable batteries.
  • Nickel-Cadmium: Popular in the 1970's, NiCD batteries where the first readily available rechargeable cells in common use. The biggest issue was the toxicity of cadmium, which led to them largely giving way to the more environmentally friendly NiMH chemistry in the 1990's. 
  • Nickel Metal Hydride: NiMH batteries were a drop-in replacement for NiCD. They offer similar battery life and operating characteristics, including the same 1.2 Volt output in AA form without the toxicity.
  • Lithium: Lithium batteries provide high energy density and higher voltages, but also carry the chance of overheating with possible results including fire or even explosions. It's also relatively difficult to make a drop-in replacement for AA as you can with NiMH batteries.

Why Use NiMH Batteries?

NiMH offers a number of benefits as a rechargeable battery technology, and also a number of tradeoffs. In most cases the advantages of these rechargeable batteries are enough to swing the pendulum over to their side:

  • Compatibility: NiMH rechargeable AA batteries are compatible with almost any application that uses AA cells. Their 1.2-Volt standard output actually matches the average output of alkaline batteries, and you can combine them in NiMH rechargeable battery packs for a variety of uses.
  • Discharge: While the stated voltage is lower, NiMH batteries actually have better sustained discharge capacity than alkaline, so they can power high current draw devices such as cameras for longer periods of time. They self discharge more rapidly, so you have to recharge them if they've been sitting on the shelf, but rechargeable cells provide more total power under heavy use.

Using NiMH Batteries

One catch with NiMH, and NiCD, is that the batteries are more difficult to recharge than other rechargeable batteries. They don't have a float voltage, so it can be harder to detect a full charge with NiMH and stop the recharge process than with other rechargeable chemistries. The easiest way to do it is with a slow charger, you can just put your NiMH cells on charge overnight and they will come up charged in the morning.

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