NiMH batteries are similar to Ni-Cd batteries with hydrogen absorbing negative electrode. These batteries have higher capacity as compared to Ni-Cd batteries and are typically used for applications where high drain current is required, such as in a digital camera. High drain applications are those where a large amount of power is required over a short span of time. NiMH is able to do well in this area because of its lower internal resistance.
NiMH batteries have the highest self-discharge rate, typically 30 percent per month. However, if longer shelf life is required then Low Self Discharge (LSD) NiMH batteries are available whose self discharge rate is as low as 2 percent per month. LSD NiMH batteries come at the cost of lesser capacity for the same size as compared to a normal NiMH battery.
A NiMH battery has the same nominal voltage as NiCd battery i.e. 1.2V per cell. A NiMH battery does not suffer from the memory effect problem but has, in addition, Self Discharging issues:
• Exposure to high temperature: At higher temperatures, chemical reactions tend to accelerate the aging process within the battery. Also, at elevated temperature NiMH batteries tend to discharge faster.
• Cell Reversing: Same as discussed with Ni-Cd battery.
Lead Acid Cell:
As the name implies, this battery uses lead-derived materials for the electrodes and an acidic solution for the electrolyte. It uses Lead Dioxide and porous lead for the positive plate and negative plate of the cell respectively in an electrolyte of Sulphuric Acid (H2SO4). Use of heavy metal elements makes this battery toxic and hazardous if not properly disposed of.
Lead acid battery is one of the most popular and extensively used batteries in the industry because they are robust and low cost. They are available in various variants to suit the needs of many end-applications. The biggest market for the lead acid battery is the automobile industry where high current drive is required. In such applications, the battery is used for starting the engine and to provide charge when electricity generated by the alternator is not sufficient to meet load requirements. Because of the application requirements, batteries used in automobiles are not designed for full discharge.
For applications which require deep discharge, thick plates are used for the positive and negative electrodes. This increases the resistance of the plates which in turn reduces the peak current but makes them capable of withstanding frequent discharge.
Lead acid batteries can be shipped without electrolyte; this provides a distinct advantage of “infinite” shelf life. Each lead acid cell provides 2.1V and is stacked together to come in wide range of sizes and capacity. These batteries, however, suffer from the following problems:
• Gassing: When the battery is charged faster or more than what it can absorb, the excessive energy is turned into heat which causes the electrolyte to boil and evaporate. This causes the production of Hydrogen and Oxygen. Sealed batteries are designed to recombine them into water, thus prolonging the life of the battery, but in case of batteries with vents, loss of electrolyte may create explosive conditions and can permanently damage the battery. Therefore, these batteries, require regular maintenance of their water level.
• Sulfation: This is a product of deep discharge which causes the crystallization of lead sulphate on the battery electrodes. It hinders the recharging of battery and may permanently damage the battery by expanding further causing short circuit between the two electrodes. Sometimes this can be corrected by equalization where the battery is overcharged in a controlled environment to boil the electrolyte and gas to break the bonds formed because of sulfation.
• Corrosion: Corrosion of the external metal contacts occurs because of different materials being used for the contacts. Because of overcharging or spillage of electrolyte, sulphuric acidic fumes or electrolyte reacts with the metal and makes it corrode.
I was looking at my neighbor's outdoor solar lights last night and I was surprised to see NiCad batteries in what is supposed to be a green product. I assume they have the cheapest charging method, which would be trickle charge.
Look at the inverse correlation between the level of Depth Discharge and discharging cycles at that article.
Besides, part II of this article finally did not answered most questions left unresolved here. This link http://blog.bestlaptopbattery.co.uk/ might prove to be more useful than what we are commenting into.
The focus of the aricle is on recharable batteries.
There is a whole peletora of non-rechable batteries that are available off-the shelf. These includes:
Carbon Zinc 1.5V
Alkaline Manganese 1.5V
Lithium Iron Disulphide 1.5V, long shelf life, high power density
Lithium Manganese 3V, long shelf life, high power density
Lithium Thionyl Chloride 3.6V, long shelf life, very high power density
Silver Oxide 1.5V, typically button cells only
As mentioned above there are regulatory requirements to consider when selecting a battery technology. There are issues with batteries based on cadmium, lead, and lithium (and mercury, of course) in a variety of markets, not just the EU. Some are environmental, some are transport-related.
If you're going to do an article about "Selecting the right battery" in 2012, consideration of environmental performance, recyclability, potential shipping constraints, and legality are of critical importance.
Why do you leave that much reserve capacity in the battery? Is it to extend battery life? Is it because the internal impedance goes up too much? I remember when the voltage gets down near 3V, the battery is going fast.
Here are a few other good characteristics of lithium ion batteries: flat discharge curve, typical voltage just about right to linear regulate for logic, and it's easy to detect charge termination. Low self discharge is important for many low power applications.
You don't have to use CC/CV charge methods for these batteries. You can pulse charge them.