Why Go Rechargeable? Part 2
Rechargeable battery types: NiCd vs. NiMH, and why there are no Li-ion AAs

Erica A.

Monday, November 03, 2008

2. Rechargeable battery types: NiCd vs. NiMH, and why there are no Li-ion AAs

There are two types of rechargeable batteries in standard sizes: NiCd and NiMH. NiCd, which are nickel-cadmium based, were the first rechargeable batteries available to the public. They’re often referred to as “NiCads,” but that’s actually a brand name.

NiCds were first invented in 1899 in a non-portable form (kind of defeating the purpose), and didn’t enter widespread production in the U.S. until the 1960s. Your first RC car likely had NiCd batteries.

One disadvantages of NiCd batteries is that they suffer from the memory effect. This means that a NiCd that has been charged and discharged a number of times loses its charge more quickly than a newer NiCd battery. This is caused by the buildup of cadmium crystals inside the battery. To prevent this, NiCd batteries should only be placed in their chargers after they are fully discharged.

Another disadvantage is that NiCds also contain toxic materials like cadmium and mercury. For this reason, the sale of NiCds has been banned in the European Union except for select purposes.

	Pros	Cons
NiCd	-Lower Price	-Memory Effect -Self discharge quickly, but not as quickly as NiMH -Contains toxic materials
NiMH	-Higher total capacity than NiCd -No memory effect	-Self-discharge more quickly than NiCd -Can generate more heat than NiCds

The most common everyday use rechargeable batteries are nickel metal hydride batteries, or NiMHs. They were developed in 1989 as an alternative to clunky nickel-hydrogen batteries, which are mostly used in satellites today. NiMHs are much less toxic than NiCds. Due to their low price and relative eco-friendliness, NiMHs are currently the most popular rechargeable option.

You may know that lithium-ion (Li-ion) rechargeable batteries incased in battery packs are widely used in electronic devices like cell phones, laptops and mp3 players. Why aren’t there any lithium-ion standard-size batteries to substitute AA size alkalines? Li-ion batteries run at a higher 3.6 voltage than standard aa size batteries usually do 1.2 volts; that makes them incompatible with both your devices and battery chargers. Plus, due to the high energy and high heat potential, they need a PCB board to control current and over voltage for them to be used safely and effectively.

What about rechargeable alkaline batteries? Generally speaking, rechargeable alkalines cost as much as superior NiMH rechargeables, and have a much shorter lifespan—dozens of recharges rather than hundreds. For more detail, Michael Bluejay elaborates here.

Part 1: Why Go Rechargeables: A Mini Blog Series

Part 2: The Different Kinds of Rechargeables

Part 3: Save money in the long run

Part 4: Heavy metal: Rechargeables and the environment

Part 5: Max Power: Take your rechargeable use to the next level

Why Go Rechargeable? Part 2 Rechargeable battery types: NiCd vs. NiMH, and why there are no Li-ion AAs