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F.A.Q.
- What types of battery are available and what are their applications?
- How do different batteries rank in terms of performance and cost?
- How should I strike a good balance between performance and cost when selecting batteries?
- What is the voltage of a rechargeable battery?
- Are primary batteries fully replaceable by rechargeable batteries even though they are 1.2 volts?
- What are the advantages of using rechargeable NiMH batteries?
- What are the factors affecting the performance of NiMH batteries?
- What is a short circuit and what are its consequences?
- What is the difference between rechargeable battery chemistries?
- Fast charging vs slow charging, which is better?
- What is trickle charge?
- How do I select a charger?
- How long will it take to charge my batteries?
- Can I charge batteries continuously?
- My batteries get warm during charging, is there something wrong?
- What is memory effect?
- Do NiMH batteries have memory effect?
- What is the self-discharge rate of NiMH batteries?
- What is cycle life?
- What affects cycle life performance?
- How do I maximize battery service life?
- How should I store NiMH batteries?
- Do warm and cold temperatures affect batteries?
What types of battery are available and what are their applications?
Batteries are usually classified as primary batteries and rechargeable batteries.
Primary batteries are sometimes called "throw-away" batteries because they will be discarded when they are flat, as they cannot be recharged for reuse. Common types of primary batteries include alkaline, zinc carbon, lithium, silver oxide and zinc air batteries.
Rechargeable batteries can be recharged and reused for up to 1000 times depending on usage conditions. Common types of rechargeable batteries include Nickel Metal Hydride (NiMH), Nickel Cadmium (NiCd) and Lithium Ion (Li-ion) batteries.
How do different batteries rank in terms of performance and cost?
You may have come across terms like "heavy duty", "super heavy
duty", and "longer lasting". However, they do not necessarily
reflect the service time of batteries, as battery performance
depends very much on intrinsic qualities.
Despite the higher initial cost, alkaline batteries last five to
ten times longer than zinc carbon batteries on higher current
drains, making it more economical when the current drain is
high.
Rechargeable batteries are more expensive than alkaline batteries especially when you include the upfront cost of the charger. However do not forget that they can be recharged up to 1000 times. Hence they end up much more economical in the long run.
NiCd and NiMH batteries display similar characteristics, but for the same size, NiMH batteries can double the run time compared with NiCd batteries per charge.
How should I strike a good balance between performance and cost when selecting batteries?
To be a smart consumer, you have to understand the power consumption requirement of your electronic device before deciding on which battery to go for. Generally speaking, high power consumption electronic devices operate under high current condition.
NiMH batteries will provide the longest operating time. Besides, they can be recharged up to 1000 times. Hence the cost per unit energy is much lower than alkaline and carbon zinc batteries.
Alkaline batteries are best used for moderate power consumption electronic devices.
Zinc carbon batteries are the best choice for extremely low power consumption electronic devices.
What is the voltage of a rechargeable battery?
NiMH & NiCd batteries share the same nominal voltage of 1.2V per cell, whereas batteries using a different type of chemistry system: Lithium ion batteries provide a voltage of 3.6 - 3.7V.
Are primary batteries fully replaceable by rechargeable batteries even though they are 1.2 volts?
Yes, NiMH batteries are ideal substitutes in most cases, especially in high power consumption electronic devices.
Although alkaline batteries are rated at a nominal voltage of 1.5 volts, as they begin discharging, their voltage continuously drops. Over the course of discharge, the average voltage of alkaline batteries is in fact about 1.2 volts, very close to NiMH batteries. The main difference is that an alkaline battery starts at 1.5 volts and gradually drops to less than 1.0 volt, while NiMH batteries stay at about 1.2 volts for most of the service time.
What are the advantages of using rechargeable NiMH batteries?
Performance
NiMH batteries can be more than three times longer lasting than
alkaline batteries in high power consumption electronics
devices.
Savings
They can be recharged for up to 1000 cycles, giving you tremendous
savings in the long run.
Environmentally friendly
They do not contain hazardous materials, such as cadmium or
mercury, and therefore are more environmentally friendly.
What are the factors affecting the performance of NiMH batteries?
Short service time of NiMH batteries is very often the result of
consumers' lack of understanding and knowledge of the importance of
proper charging on battery performance.
Both overcharging and over discharging the batteries will result in
poor battery performance.
Improper charging can also reduce the cycle life (the number of times the batteries can be recharged) of NiMH batteries. In addition, avoid using NiMH batteries at high temperatures, as their service time will be reduced.
What is a short circuit and what are its consequences?
A short circuit occurs if the positive and negative terminals of the battery are bridged by any kind of conducting materials e.g. key chains, paper clips. Short circuits may have serious consequences. For example, the battery temperature will rise, causing internal gas pressure to build up and eventually resulting in battery leakage.
To avoid short circuits, do not carry charged or fresh batteries in the same pocket with coins or bunches of keys.
What is the difference between rechargeable battery chemistries?
Lithium Ion (Li-ion) batteries have increased capacity and are very lightweight. Their nominal voltage is 3.7V.
Nickel Metal Hydride (NiMH) batteries offer high capacity (over twice the amount of Nickel Cadmium (NiCd) batteries), quick charging capabilities and great reliability. They are especially good for high drain applications like digital cameras and motor toys. They are also suitable for CD players, MD players, and MP3 players etc. The nominal voltage of NiMH batteries is 1.2V.
Nickel Cadmium (NiCd) batteries have a longer cycle life, though shorter run-time than NiMH batteries. They are the most cost effective rechargeable batteries and can last up to 1000 charges. They are hardy and can withstand very low temperatures and rough use. Like all rechargeable batteries, NiCd batteries need to be completely charged before their first use. The nominal voltage of NiCd batteries is 1.2V.
Fast charging vs slow charging, which is better?
Fast charging employs a high charging current which enables you to charge up a NiMH battery in a relatively shorter time, ranging from five hours to even half an hour.
Using a low charging current, slow charging often refers to overnight charging, which normally takes over 12 hours to charge up a NiMH battery.
However, the time it takes to fully charge a battery depends on the charging current of the charger and the capacity of the battery.
Imagine filling up a bucket under a running water tap. The bigger the bucket, the longer it takes to fill it up. You can also increase the rate of filling the bucket by turning up the tap a bit more.
Trickle charge refers to an extremely low charging current that is enough to keep the batteries in fully charged condition but without overcharging the battery.
Fast chargers and slow chargers have their respective merits and demerits. You should choose a charger that meets your performance and cost requirements.
A fast charger delivers speed, but its design is more complicated, and therefore is usually more expensive than a slow charger.
Overcharging can shorten a NiMH battery's cycle life. Hence a well-designed fast charger has to incorporate certain protection mechanisms that prevent the batteries from being overcharged.
These protection mechanisms, ranging from sophisticated voltage detection to temperature monitoring and timer control, can be expensive. Normally a fast charger has to incorporate at least one of these mechanisms. The more mechanisms it has, the better the protection and thus the higher the price.
Therefore, when charging speed is not a priority, it would be more cost effective to select a slow charger, which also gives longer battery service life and enables fuller charge of a battery compared with a fast charger.
However, for applications that require fast charging speed, e.g. remote control racing toy car and digital cameras, it would be worthwhile to invest more for a fast charger to ensure continuous supply of energy.
How long will it take to charge my batteries?
This depends on two factors: the charging current, which is measured in milli-ampere (mA) and the capacity (mAh) of your battery.
Assuming that the charging current is the driving speed and the capacity of the battery is the total distance you have to travel. Then the time required to charge up your battery would be ...
Capacity of battery / charging current X 120%
Usually you inflate the charging time by about 20% for any efficiency loss during charging.
Can I charge batteries continuously?
Yes, depending on the design of the charger. Theoretically a NiMH battery can be charged continuously in a charger at 0.1C, which is a very low rate of charging.
My batteries get warm during charging, is there something wrong?
No, it is normal for batteries to get warm during charging.
Memory effect occurs when the battery is charged before its energy is fully consumed. The battery will remember its last residual capacity before it is recharged. Hence if you keep on charging the batteries before you have used up the energy, the service time of each cycle will get shorter and shorter.
Do NiMH batteries have memory effect?
The present day technology enables NiMH to have either no or negligible memory effect.
What is the self-discharge rate of NiMH batteries?
If a NiMH battery is left idle after being fully charged, it will gradually loses its energy. This is called self-discharge. In general, the rate of self-discharge ranges from 15% to 20% per month at room temperature.
Cycle life is the number of charge and discharge cycles a battery can achieve before the discharged capacity drops to end of life. The cycle life is generally considered to terminate when the capacity is less than 60 - 80% of the nominal capacity, depending on the specific charge / discharge conditions.
What affects cycle life performance?
The following factors may affect a battery's cycle life:
Charge
You are recommended to charge the batteries with appropriate
chargers equipped with correct charge termination methods (such as
timer, negative delta voltage and temperature cut-off), so as to
avoid the possibility of shortened cycle life resulted from
overcharging. Generally speaking, slow charging would lead to
longer cycle life than high rate charging.
Discharge
The dominant variable affecting cycle life is the depth of
discharge. The deeper the depth of discharge, the shorter the cycle
life. By decreasing the depth of discharge, the cycle life of a
battery will be significantly increased. For this reason, it is
necessary to avoid over-discharging of batteries to a very low
voltage. Depending on different discharge currents, 0.8-1.0V per
cell is the generally acceptable end point voltage.
Discharging battery at high temperatures will reduce the cycle life.
Batteries can sometimes be drained excessively by small residual currents in idle equipment left for extended periods, if the design of the equipment does not shut down all currents completely.
Using battery with different capacities, chemistries, charge levels or using old and new batteries together can also cause over-discharge.
Storage
If a battery is stored for a long time at a high temperature, the
electrode will deteriorate, reducing the cycle life.
Avoid leaving a battery in a charger for an extended period.
How do I maximize battery service life?
To maximize the cycle life of batteries, you should:
Store the battery in a cool, dry and well ventilated place out
of direct sunlight. The ambient temperature should be kept below
30degC for long-term storage. Prevent charging or using batteries
in extreme temperatures.
Charge the batteries with correct chargers to minimize the chance
of overcharging. Choose charger with appropriate charge control. It
is recommended to purchase batteries plus charger bundle
packs.
Charge and discharge the battery occasionally to prevent the
battery voltage from dropping down to 0.8V.
Remove batteries from an equipment or turn off the equipment if it
is not to be used for a period of time.
Avoid overcharging the battery by exceeding the predetermined
charging period specified by battery manufacturer.
Avoid mixing batteries of different chemistries, capacities and
state of charge in the same devices.
How should I store NiMH batteries?
In general, the higher the storage temperature, the worse the capacity retention of NiMH batteries.
