Ah, how time has passed since the invention of the nickel cadmium-based rechargeable electrochemical batteries that my father used until quite recently. Invented in 1899, the rechargeable battery (also known as a secondary cell) was made available commercially in the 1950s. Pretty puny in terms of today’s devices; it was time for them to evolve. Next came nickel-metal hydride (NiMH) cells, lithium ion (Li-ion) cells, lithium polymer (Li-Po) cells, used in computers, and lithium phosphate cells (still in the early stages of development). The reason that rechargeable electrochemical cells have had to evolve so quickly is due to increased energy demands: digital cameras, among other examples, are energy hogs.
A few definitions from the Canadian Oxford Dictionary
Battery: noun 1 a device, consisting of one or more cells, in which chemical energy is converted into electricity [French batterie from batre, batter strike, from Latin battuere].
Cell: noun 7. Electricity a battery or other device for generating electricity or producing electrolysis from chemical energy.
Electrolysis: noun 1 chemical decomposition produced by passing an electric current through an electrolyte.
Electrolyte: noun 1 a liquid, esp. that present in a battery, which contains ions and can be decomposed by electrolysis.
Voltage represents power or brute force, metaphorically speaking. Picture a big guy pushing his broken-down car. He has to use great strength, which is evaluated in Volts in the case of a rechargeable battery. You will notice that all rechargeable batteries have a tiny 1.2 Volt current, which is perfectly fine for driving our little Mini Cooper, which represents our digital cameras.
Electrical Charge (mAh)
This is what we’re most interested in: electrical charge. In my analogy about the guy whose car broke down, it is important that our guy be able to push hard enough to move the car; but if he cannot push it for long, his strength becomes useless. The symbol mAh stands for milliamp hours or the energy that a rechargeable battery can produce in a given time. We are looking for batteries that produce the most mAh to keep up with our highly demanding digital devices.
Even today, nickel cadmium AA cells rarely deliver more than 1100 mAh, which explains their quick loss of charge in a world where electrical independence is crucial. What’s more, they have this weakness called the “memory effect” that causes them to become less efficient over time (see sidebar). Due to their lethal chemical composition (cadmium is a highly-toxic heavy metal), laws have appeared, more particularly in France in 2006, banning their public use.
Happiness has arrived in AA format. They produce an electrical charge of up to 2900 mAh that enables two rechargeable NiMH cells to take close to 400 shots, with certain camera models (Canon Powershot A2100, tested according to CIPA standards). In addition, there is no memory effect: you can recharge these cells whenever you wish, without worrying about causing damage. The absence of cadmium makes them greener than their NiCd cousins.
The lithium-ion cell is nothing more than a replacement for the NiMH, which does not exist in AA format. The lithium-ion was designed and moulded to fit inside whatever device it powers. We often talk about “proprietary” formats. Other than their distinct shape, these match the definition of a rechargeable NiMH cell: powerful and without memory effect.
These three types of rechargeable batteries lose their charge when stored. Lithium-ion cells can lose up to 10% of their charge per month, NiCd cells up to 20%, and NiMH cells 30%. Three months of sitting in the bottom of a knapsack will kill these energy sticks. That is why the new NiMH techno logy on the way does not have this inconvenience. These super secondary cells, which have a nominal charge capacity above other NiMH cells (around 2100 mAh), keep 85% of their electrical capacity after a year of storage. Simply put, they are energy camels. They use the same type of charger as other NiMH batteries.
Number of Cycles
Nothing lasts forever in this world. I can feel my youthful energy slipping away slowly. Your cells are doing the same thing, from being used. We often hear about the “number of cycles”. You use secondary cells and you recharge them: that counts as one cycle. According to the manufacturers, their life ends after 500 to 1000 cycles. (A personal observation: the majority of lithium-ion cells last about four or five years, no matter what you do. NiMH cells survive for between two and four years, depending on the quality of the chemicals used.)
So, Lithium-ion or NiMH?
Not that we have a say in the techno logy our camera uses (it’s one or the other), but we can ask for help in choosing a new camera according to the type of rechargeable batteries involved. In terms of available energy, these two rechargeable cell types are the same. There are many AA-format fanatics; among them are travellers to desert-filled countries, who like to horde alkaline batteries (available worldwide) in case the power goes out. On the other hand, there are lithium-ion cell lovers who are looking for a better weight/efficiency ratio. Their cameras are lighter and more compact, but to be on the safe side they have to buy another rechargeable cell, one that could cost them close to $70. Who is wrong? Who is right? It doesn’t matter… just make sure you’re not working with them in the wrong way.