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| Frequently Asked Questions |
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What are the different types of battery?
Batteries are classified into two groups, primary and secondary.
Primary batteries cannot be recharged, and once they have gone flat they have to be thrown away. Primary batteries include Zinc Carbon, Alkaline, Lithium, Silver Oxide (used in watches) and Zinc Air batteries (used in hearing aids). Secondary batteries can be recharged and used again and again, up to 1000 times. The commonest type of rechargeable battery is the Nickel Metal Hydride, but Nickel Cadmium and Lithium Ion batteries are also available.
How do I decide which battery to use?
For many applications, although not all, the decision will come down to a tradeoff between cost and performance. Each type of battery chemistry has its own advantages and disadvantages and your choice will largely depend on how you intend to use the battery.
Zinc Carbon batteries are cheap but they have little capacity and they soon run out. They are suitable for devices where the demand is low and infrequent.
Alkaline batteries are more expensive, but generally last five to ten times longer than Zinc Carbon batteries and so they provide better value for money. They are useful in devices where the current drain is higher, such as torches.
Lithium batteries are similar to Alkalines; they are more expensive and last up to seven times longer. They are particularly useful for digital cameras and flash guns. They have a long shelf life of up to fifteen years.
Rechargeable batteries are more expensive than Alkalines, and in addition they require a charger. They are a sound investment however because they can be recharged between 300 and 1000 times, each charge costing less than one penny’s worth of electricity. Nickel Cadmium batteries are being phased out as cadmium is highly toxic and for this reason these batteries cannot be disposed of in land fill sites in case they pollute the water supply. Nickel Metal Hydride batteries hold more power than Nickel Cadmiums and for that reason alone they are superior to Nickel Cadmiums.
So which battery type is the best value?
This depends on what you are going to use them for.
Nickel Metal Hydride batteries are the best for high drain, frequent use such as digital cameras and portable CD players. They not only provide a longer operating time but they can be recharged up to a thousand times, producing enormous savings. If you get through a lot of batteries you should seriously consider these.
Lithium batteries are suitable for the same devices. They are long lasting and reliable, and very convenient.
Alkaline batteries are best for devices that have moderate power consumption. Although Zinc Carbon batteries can be used for low consumption devices, Alkaline batteries will last far longer and in the long run they provide better value.
Do all batteries provide the same voltage?
Rechargeable batteries provide a nominal voltage of 1.2V while Alkaline provide 1.5V. The voltage provided by Lithium batteries varies depending on the type. Notice the use of the word ‘nominal’. What actually happens is that as soon as you start to use an alkaline battery the voltage gradually drops, until it reached just under one volt. By contrast a rechargeable battery will provide a steady voltage of 1.2V until it is almost exhausted, when the voltage will fall fairy quickly. The average voltage supplied in both cases is 1.2V and in practical terms the variation in the voltage is not significant and will rarely produce any noticeable effects.
What are the benefits of rechargeable batteries?
The most obvious advantage is the cost. You can buy a charger and four batteries for under £20 which will provide a minimum of 300 charge recharge cycles, each charge costing 1 penny and providing the equivalent power of four alkaline batteries. Total cost £23, as against a minimum of £450 for the alkaline batteries they replace.
In addition, because their voltage drops slowly during discharge they will last longer than alkaline batteries in devices such as digital cameras.
One set of rechargeable batteries will replace at least three hundred sets of alkaline cells, producing enormous savings in the energy consumed as well as the materials used in their manufacture.
Nickel Metal Hydride batteries do not contain any toxic materials and are environmentally friendly.
How should I take care of my rechargeable batteries?
Overcharging can affect battery performance. This can be avoided by timing the charging process or by using electronic chargers which continuously monitor the battery’s charge status and switch to a trickle current once the battery is fully charged. Short circuiting can permanently damage batteries and you should avoid carry them in your pockets in case of contact with keys or money.
What are the different types of rechargeable batteries?
There are three main types. Lithium Ion batteries are used in digital cameras and laptop computers. Nickel Cadmium batteries can be recharged more times than Nickel Metal Hydride and they are economical, however they are being phased out due to their toxicity.
Nickel Metal Hydride batteries have a high capacity and can hold over double the charge of Nickel Cadmium cells. Although they are particularly useful for high drain devices they can be used in anywhere you would normally use alkaline batteries.
What is the best charger to buy?
There are two things to look at when buying a charger. The first is the charge time. Generally speaking, faster chargers are more convenient but slower chargers make for a longer battery life. Which one you choose depends on how you intend to use the charger.
The second is what protection the charger provides against overcharging, which can shorten the battery’s life. The simplest chargers have no protection at all; they rely on you to switch the charger off after a specified time. More expensive chargers will incorporate an electronic timer, while the most expensive will use special sensors to identify when the battery has been fully charged, and automatically switch off the current. These detectors either monitor changes in the battery’s temperature, or internal voltage, or both to tell when the battery is fully charged and they usually switch from a charge current to a trickle current. This will keep the battery topped up until it is taken from the charger. Good quality chargers will monitor each battery individually and independently.
Regarding the costs of the charger, the faster the charger the more important it is to have proper control of the charging process, and the more expensive the charger will be. Charging times range from fifteen minutes to sixteen hours, but more typical is one to two hours for fast chargers and eight hours for overnight ones.
Why do the batteries become warm when charging?
This is normal and is a result of the chemical reaction taking place as they are charged. Fast charging is more likely to warm the batteries and some fast chargers include a cooling fan.
How long does it take to charge batteries?
This can be calculated from two figures, the charging current in milliamps and the capacity in mAh (milliamp hours). In theory, the charge time is the capacity divided by the charging current. For instance, a 2500 mAh battery supplied with a 500 milliamp current will take five hours to reach full charge. In practice it is a good idea to add on 10% to the calculated charge time. If you want the charge time to be calculated please send an email: info@dolphinbatteries.co.uk
What is the memory effect?
This occurs with Nickel Cadmium batteries which are incompletely discharged before being recharged. Once affected, the batteries do not hold a full charge. Nickel metal Hydride batteries are not affected.
What is self discharge?
If NiMH batteries are left unused they will gradually lose their charge. This is typically at the rate of 10% to 20% per month. The batteries should be charged before first use, and recharged if not used for more than a month or so to keep them in good condition.
How long will my batteries last?
Nickel Metal Hydride batteries will normally last for between 300 and 1000 charge-recharge cycles. When first used the batteries have to be charged three or four times before they will hold their full capacity, however after that they should hold a full charge for hundreds of recharge cycles. Eventually however this capacity starts to fall and the battery’s life is ended when it will hold only 60% of its rated capacity.
What can I do to maximize the battery’s cycle life?
It is important to use a good quality charger that monitors the charging process and switches to a trickle charge when the battery is fully charged. Various methods are available; the simplest is to use a timer but there are also chargers which can detect changes in temperature and voltage. If your charger doesn’t use any of these methods then you can calculate the charge time yourself.
The speed of charge will affect cycle life; the slower the charge the longer the life expectancy. In addition, lower capacity batteries will have a longer life than high capacity cells.
How far the battery is discharged before being recharged will also affect cycle life. Over discharging the batteries will shorten their cycle life, conversely recharging the batteries before they reach this state will increase the cycle life. It is a good idea to remove batteries from devices when they are not in use in case they are affected by any residual currents. Batteries can also be over-discharged if they are used with other batteries at different voltages.
Good housekeeping tips.
1. Always use good quality battery chargers. If possible use electronically controlled chargers but if not calculate the charge times to avoid overcharging the batteries.
2. Do not mix batteries of different chemistries, sizes, or charge states.
3. Remove batteries from the equipment if they are not going to be used for some time.
4. Always recharge the batteries before they become fully depleted.
Rechargeable batteries are a sound economical alternative to conventional batteries, and with proper use your batteries and charger will give many years of reliable service, and in the process save you a considerable amount of money.
If you want help in calculating the charge time for your batteries please email us with the capacity of your batteries, and the current supplied by your charger.
If you have any further questions about batteries email: info@dolphinbatteries.co.uk
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