Wednesday, May 11, 2016

Let's talk about Battery - AA

Good evening everyone, I'm planning to start a new segment on batteries, might be boring to some people but some might find it interesting. First post of this series I think should be about the ubiquitous AA Cell. 

AA battery:

Let's start with a little bit of history. It is a dry battery, though dry battery was developed in 1866 the AA battery was first introduced in 1907 and they are still around 100 years later. It was standardized in 1947 by ANSI. Ever ready manufactured the first AA battery. ANSI specifies this battery as size 15 where IEC calls it by R6. You might have seen LR6 written on too, it means the battery chemistry is Alkaline where the R6 refers to standard Zinc-Carbon chemistry(actually R stands referring round battery but if L is not present it means the chemistry is Zinc-Carbon). Alkaline-manganese batteries were developed in 1960 however, which has much higher capacity compared to the Zinc-carbon batteries.

What defines AA battery?

AA cell has a standard size which is 49.2–50.5 mm in length and 13.5–14.5 mm in diameter. There is also rules for positive button terminal to have a minimum 1 mm height with maximum 5.5 mm diameter and the negative flat terminal can not less than 7mm in diameter. These strict rules are maintained to make sure that devices can be designed to use these cells without any issue of compatibility.

AA cells have different capacity and mass depending on brand and chemistry although the Zinc-Carbon and Lithium Ions are on the lighter side where the rechargeable Nickel–metal hydride are on the heavier side, not to mention the Alkaline cells are in the middle of this mass based categorization. 

Different chemistries and Brand!

Although AA has distinct size but it might be based on many different chemistry which might have different open circuit voltage and different capacity. Starting with the most common one, Zinc-carbon first commercial dry battery. This chemistry has made portable flash-lights, radios etc possible.

Typical capacity of a Zinc-Carbon battery under a 100mA drain might be about 300-1700mAhr. Very common Sony New ultra batteries have about 600mAhr capacity where the Toshiba Extra Heavy Duty might provide around 900mAhr. There was a time when I mostly used the National Hyper cells and those were amazing. They were better than the Sony Super battery of that time. Later I used Maxell, Toshiba and Panasonic batteries. Those were good too but according to my testing the Sony cells seem to last much less than the other names that I have mentioned.

Next chemistry that is popular is the Alkaline one. The major problem with Zinc-Carbon was the small capacity and low peak output current. Alkaline can provide much higher current if needed in device like Flash light of camera and has significantly more capacity while driving low drain devices such as a Quartz wall clock. Right now this one is probably the most used one, although Zinc-Carbon is still around as they are very cheap.

The very first Alkaline that I used was the Kodak Photo Life. Which was just amazing. Later I tried out the Energizer Alkaline which was awesome too. This days however I mostly use Duracell and Kendal Alkaline cells which are good too. Typical Duracell, Panasonic and Maxell alkalines might have a capacity of 2300mAhr, 2500mAhr and 2400mAhr respectively. Both Zinc-Carbon and Alkaline have nominal voltage of 1.5V so they are very much compatible with each other. Both these cells are better suited for low drain applications like wall clocks, Television Infra-red remote controller, portable radios, torch lights etc. One of the positive things about Alkaline is their high shelf life. You can just keep them stored in somewhere suitable and they will retain their charge for years after years.

So these two were the most common types of cell but both of them have the same issue. They are disposable and doesn't have good high drain performance. Hence the need for a rechargeable cell was obvious and Nickel-cadmium and Nickel Metal Hydride was born. Ni-Cd was the older one and they can have a capacity of 1000mAhr with a maximum of 2000 times charging capability which made them ideal for many devices that consume more power. These cells are cost effective. But there was two problems with them, first one is the use of Cadmium which is bad for Human and environment and Ni-Cd has a nominal voltage of 1.2V as oppose to 1.5V on Zinc-Carbon or Alkaline-Manganese.

to be cont.