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Battery Part 2: Types of batteries

Patent case camera 1824 Let's take a look at the various types of battery available for digital cameras starting with the zinc-carbon cell or the standard dry cell. It comes in the standard cell size of AA, AAA, C and D. Just like its name, the zinc-carbon cell's electrodes are made of a zinc can and a carbon rod and the chemical used is acidic paste. The zinc-carbon cell is a low current, low power density and low energy capacity battery suitable for running radios, smoke detectors, clocks or any low power appliances. Try it on your digital camera and it will go from full power to zero power in just 2 minutes! The good thing about zinc-carbon cell is its low cost and a medium self-discharge rate with a shelf-life of 2~3 years.

30/Pack alkaline battery
30 per pack alkaline battery
The most popular battery capturing over 50% of the market share is the alkaline battery. The electrodes in alkaline battery are made of zinc powder, carbon conductor and a mixture of manganese-oxide and the chemical is alkaline based, often referred to as alkaline-manganese battery.

Alkaline battery has good energy capacity but medium power density. The standard alkaline battery is suitable for most household appliances, may be used as an emergency power source for digital cameras (about 10 to 15 shots per set of battery). The high-end alkaline battery such as Energizer "Advanced Formula" or Duracell's "Ultra" has about 40% more power than the standard alkaline battery. Using it for digital cameras can be quite costly in the long run and takes about 15 to 25 shots of picture per set of battery.

There are also rechargeable alkaline battery often referred to as RAM cell or Rechargeable Alkaline Manganese cell but this is not recommended for digital cameras. This rechargeable alkaline has lower energy capacity than standard alkaline. It may look attractive for the rechargeable features. However due to its low power density and unable to handle high power drain required by digital cameras, that rule them out as power source for digital cameras.

Rechargeable alkaline has a low charge/recharge life cycle of about 25-100 cycles, but a low self-discharge rate enables them to retain their charges quite well, as much as 5 years in storage! To extend the cycle life of a rechargeable alkaline battery always top up the battery before it is totally discharged. This is the exact opposite of the Nickel-Cadmium battery. RAM battery is usually rated at 1.5v at 1600mAh and standard non-rechargeable alkaline battery rated at 1.5v 2200mAh. This energy capacity figure looks impressive but their power density is far from impressive and can't handle high power surge thus making alkaline battery not the preferred choice for digital cameras!

Nikel Cadmium Battery from Sanyo
Nikel Cadmium Battery from Sanyo
For digital cameras the rechargeable Nickel-cadmium battery is a better choice than the rechargeable alkaline battery. NiCd has medium energy capacity but high power density which makes it suitable for high drain devices like digital cameras. NiCd is cost effective for the long run though initial start-up cost is high because of the need to invest in a NiCd battery charger, and the price of NiCd battery is much higher than RAM battery. Nickel-Cadmium battery can be recharged up to a 1000 cycles and rated at 1.25V 900mAH but has higher power density than Alkaline battery.

The bad thing about Nickel-cadmium battery is it has a "memory" effect. That means it should be totally discharged before recharging as they "remember" their last state of charge. For this reason never top up a Nickel-cadmium battery. Over time this "memory" effect causes the battery to hold less and less charges and eventually shortens the battery's life.

Nickel-cadmium battery has a high self discharge rate. It loses about 1% of its charges per day when not in use so over a month it could lose as much as 1/3 of its power in storage. Storing it in a cold place like a fridge or freezer can lower down this effect. If you choose to store them in a fridge keep them tightly sealed in a plastic bag or container to keep out moisture, and always allow them to acclimatise to room temperature before use.

Nickel-cadmium is a mature technology and probably a sunset technology. It is losing market share to other newer technology due to its "memory" effect, and most of all the toxic environmental impact of cadmium when disposed. When disposing Nickel-Cadmium battery - read the manufacturer's instructions. Some manufacturers may accept dead Nickel-cadmium battery for recycle. Most battery manufacturers have stopped producing NiCd and switched their production to Nickel-metal hydride battery.

Panasonic Nickel-metal hydride battery and charger
Panasonic Nickel-metal hydride battery and charger
To overcome the "memory" effect of the NiCd battery and the adverse environmental impact of cadmium when disposed, the Nickel-metal hydride battery was developed as a replacement. Nickel-metal hydride does not suffer from the "memory" effect and does not contain toxic cadmium.

However NiMH battery has a higher self-discharge rate than Nickel-cadmium battery. It self-discharges almost half of its charges a month depending on ambient temperature(1~3% per day) and this makes NiMH not recommended for emergency devices such as smoke detectors and heat detectors in fire alarm system. Nickel-metal hydride should be recharged monthly even not in use. Storing it in a fridge or freezer as mentioned above can slow down its self-discharge rate.

Nickel-metal hydride rechargeable has high power density and high energy capacity. At the time of writing, 2500mAh AA size NiMH can be easily found in most reputable camera stores. Nickel-metal hydride rechargeable is said to be "environmental friendly", operates over a wide temperature range, delivers high power surge on demand, high power density as well as good energy capacity and is reasonably priced. All these make Nickel-metal hydride rechargeable a favourable choice for most digital cameras.

The Lithium battery is an ideal single use battery for digital camera with its long-lasting run time and the ability to deliver power surge on demand. The lithium battery is 33% lighter in weight and delivers 5 times more power than alkaline battery, has a high power density and high energy capacity with a 10 years shelf life and performs well in a wide range of operating temperatures.

L91 Lithium battery
L91 1.5Volt 2900mAh Lithium battery
For non-rechargeable the lithium battery is almost the perfect choice for high current drain devices such as digital cameras except for the cost; the lithium battery costs many times more than the alkaline battery. For average camera users who use the digital camera occasionally the lithium battery is the best power source with its long shelf life and negligible self-discharge rate. For heavy users the Nickel-metal hydride rechargeable is a more economical alternative but do keep some spare lithium battery handy in your camera bag for the "just in case". Lithium battery comes in many shapes and sizes, from the tiny button cell to the common CR-V3, CR123 and 2CR5, also available in the standard AA size is the L91, a 1.5v 2900mAH lithium battery from Energizer.

Currently the lithium ion battery is the most ideal rechargeable for the digital camera. This compact and light weight rechargeable is "environmental friendly", withstands up to a thousand recharge cycles, high power density and high energy capacity, higher output voltage of 3.6V per cell and a very low self-discharge rate.

Well, that is not all yet; the lithium ion battery has a good power-to-weight ratio and together with its compact size enables it to pack more power into a smaller and lighter battery thus making it possible for camera designers to develop those super-thin and micro size digital cameras. The lithium ion rechargeable is also often used in cell phones and the super slim laptop computers. Wow! everything about this lithium ion is positive - too good to be true right? What is the catch then?

Well, the flip side about lithium ion battery is its high price and potential fire hazard. Condensing more power and energy into a tiny pack has its price too. The high power lithium ion may catch fire or even explode if overheated or used in wrongly configured charger or power unit. It is not advisable to leave lithium ion battery in your car boot which is subjected to high temperatures in tropical climate or during summer. If a manufacturer issue a recall for any devices that uses lithium ion battery that you may own, promptly follow instructions and return it to them and you should be entitled for a rectified replacement unit!

Research is currently in the lab to find new material to replace the cobalt oxide in the lithium ion battery which is the cause of fire and explosion. NEC/Tokin Corporation has developed a new lithium ion battery that uses manganese instead of cobalt oxide however this product is fairly new in the market at the time of writing.

The potential fire hazard and explosion of lithum ion battery is a precaution we should be aware of. Just as we are aware that gasoline or petrol in your car can also catch fire and explode but with proper precaution it is quite safe travelling in a car! If you want to know more about exploding lithium ion battery check out this PDF format InfoWorld article.

This safety issue has resulted in complex battery management circuitry to be added to the electronic thus increasing the overall cost of the battery and the devices that use it. However, this promising technology has a good future so we may see some safety improvement in the chemistry, lowering of manufacturing cost and hopefully price reduction when demand and competition catch up in the near future.

Battery not mentioned so far includes the lead-acid cells or the "car battery" as it's commonly called. The lead acid cell is bulky, heavy and contains lead and active acid making it too big and too heavy to be used in digital cameras. Many photo journalists and professional wedding photographers use a type of battery pack for their heavy duty portable flash units. The sealed lead acid cells are often found inside these power packs and some professional camcorders also use sealed lead-acid cells. The sealed lead-acid cells are also commonly used in UPS or Uninterrupted Power Supply units for computers.

Sealed lead acid battery for Camcorder
Sealed lead acid battery for Camcorder

The newer protable power source is the Fuel cell -- this technology is starting to come down in price and size. However it has a poor power density and is not ready for digital cameras in its current form. Larger fuel cell the size of a huge luggage is used in many experimental electric cars.

Mercury cell and silver oxide cell were once the main source of power for film cameras before the days of autofocus cameras and are no longer common in photography, but still used as power source for hearing aids, watches and the now hard to find manual 35mm SLR film cameras.

Next on Battery Part 3: Batteries and Cameras we will look at the various aspects of batteries and cameras, battery handling tips, safety and enviromental issues.

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