Lithium Ion batteries (Li-ion) are the most common form of rechargeable battery used in modern technology and devices. There are several reasons for this ( these will be discussed later ) but with regard to bicycle lights the main concern is the energy density or power to weight ratio. In other words how much electrical energy can be produced from a given weight of battery. In respect of this factor it is Lithium Ion batteries that are king. In a battery weighing one kilogram:
Li-ion battery can hold 150 Wh of energy
NiMH battery can hold 100 Wh of energy
Lead-acid (car battery) can hold 25 Wh of energy
The other notable advantages of lithium ion batteries is that they do not have any memory effect and they hold charge quite well when stored. Memory Effect The memory effect of a battery is a particular problem with NiMH and NiCad batteries - both of which were the most common small rechargeable battery until recently. The memory effect is a when a battery 'remembers' how much charge it previously contained and means that with batteries other than Li-ion then when they are recharged from a partially discharged state they will not accept a full 100% charge. This means that the current carrying capacity of these batteries will gradually decline unless a special effort is mode to fully discharge the battery every time it is used! Holding Charge Lithium ion batteries will lose approximately 5% of their charge per month during storage - this can be reduced by keeping in a cool place or even better by keeping them in a fridge! Some of this stored energy is used by the on-board computer that every battery pack contains (more about why this is needed later) the control computer is constantly monitoring charge and temperature so is continually using a tiny amount of energy.
The amount of energy in the battery is not the only important factor - different LED combintions can produce different amounts of light from the same battery useage - for example compare the 2000 Lumen Magicshine MJ-880 and the 1600 Lumen Magicshine MJ-872, both of which use the same amount of energy from the Li-Ion battery.
Portable equipment made use of nickel cadmium batteries for a great number of years until the early 1990s and when the lithium ion battery was brought into the market place. Although in the early days people were sceptical about its performance and reliability. However, today, demand has increased at a dramatic rate and due to its rechargeable capabilities, the Lithium-Ion battery is recognised for its cost effective way of producing power.
The initial works to perfect this type of battery began almost a century ago and the prototypes became available in a non rechargeable form much later. The initial production of a rechargeable type of Lithium-Ion batteries was hampered for some time due to safety problems. It was not until 1991 that the problems were overcome and the first of this type of battery was marketed by the Sony Corporation.
Although the safety issues have been addressed and resolved, the guidelines provided by the manufacturers have to be strictly adhered to in the interest of safety for the user. While the Lithium-Ion battery has many advantages there are a number of issues that a user should be made aware of. All batteries are fitted with a protection circuit due to the fact that it is fragile. This prevents the voltage from fluctuating to dangerous levels during charging and discharging.
Ongoing research is being carried out on the durability of the Lithium-Ion battery as manufacturers are aware of the fact that after one year, a battery can show signs of deterioration. In fact, batteries have been known to fail completely after two or three years of constant use. Research and revised chemical formulas have made vast improvements over recent years but it will be some time before it is proven that the aging concerns are completely resolved.
However, due to the improvements which are being made on an ongoing basis, the Magicshine Company recommends Lithium-Ion batteries on their extensive MJ range of bicycle lights. On a number of the lights in this range, a power indicator is fitted to advise a user when a battery needs to be recharged.
If a Lithium-Ion battery is to be stored for some time, it is recommended that a cool environment is chosen. The ideal storage temperature is 15 degrees C and in storage a battery should hold a 40% charge. Storing in this way could increase the life of a battery.
Due to the fact that the lithium ion battery requires little or no maintenance and is a lot lighter than its competitors, this is the reason that it is used in many branches of industry. Lap-top computer manufacturers take advantage of this type of battery in their quest to produce the lightest and most compact product. As in the production of a great number of portable electrical items, it has been proven that the ability to recharge far outweighs the “use and throw away” concept and the cost effectiveness of this action is endorsed by companies and customers alike.