Should I buy lithium-ion batteries?
by: Professor Mike Latreille
Lithium-ion batteries (Li-Ion) are currently one of the most popular types of rechargeable battery for portable electronics and power tools.
The main reason for their popularity is their excellent energy-to-weight ratio, meaning that they can deliver as much power as a nickel-cadmium (NiCd) battery in a much lighter package.
For users of cordless power tools, and laptop computers, the weight advantage is a definite plus.
Also on the plus side is slow loss of charge when not in use, and the fact that they don't suffer from memory effect like NiCd batteries which gradually lose their maximum energy capacity if they are repeatedly partially discharged before being recharged.
From a design standpoint, lithium-ion batteries can be formed into a wide variety of shapes and sizes, so as to efficiently fill available space in the devices they power.
DisadvantagesOne of the main drawbacks of the Li-ion battery is that its life span is dependent upon aging from time of manufacturing regardless of whether it was charged, and not just on the number of charge/discharge cycles. So an older battery will not last as long as a new battery due solely to its age, unlike other batteries. At a 100% charge level, a typical Li-ion laptop battery that is full most of the time at 25 degrees Celsius or 77 degrees Fahrenheit, will irreversibly lose approximately 20% capacity per year.
A stand-alone Li-Ion cell must never be discharged below a certain voltage to avoid irreversible damage. Therefore all systems involving Li-Ion batteries are equipped with a circuit that shuts down the system when the battery is discharged below the predefined threshold. It should thus be impossible to "deep discharge" the battery in a properly designed system during normal use. This is also one of the reasons Li-Ion cells are never sold as such to consumers, but only as finished batteries designed to fit a particular system.
Lithium-ion batteries can rupture, ignite, or explode when exposed to high temperatures, or direct sunlight. They should not be stored in a car during hot weather. Short-circuiting a Li-ion battery can cause it to ignite or explode. Never open a Li-ion battery's casing. Li-ion batteries contain safety devices that protect the cells inside from abuse. If damaged, these can also cause the battery to ignite or explode.
Guidelines for prolonging Li-ion battery life
- Unlike NiCad batteries, lithium-ion batteries should be charged early and often. However, if they are not used for a longer time, they should be brought to a charge level of around 40%. Lithium-ion batteries should never be "deep-cycled" like NiCd batteries.
- Li-ion batteries should be kept cool. Ideally they are stored in a refrigerator. Aging will take its toll much faster at high temperatures. The high temperatures found in cars cause lithium-ion batteries to degrade rapidly.
- Lithium-ion batteries should never be depleted to empty (0%).
- According to one book, lithium ion batteries should not be frozen. Note that most lithium-ion battery electrolytes freeze at approximately -40 °C, which is much colder than the lowest temperature reached by most household freezers.
- Li-ion batteries should be bought only when needed, because the aging process begins as soon as the battery is manufactured.
- When using a notebook computer running from fixed line power over extended periods, the battery can be removed and stored in a cool place so that it is not affected by the heat produced by the computer.
Buy or not?The choice is yours. Yes, there have been problems in the past with some Li-ion batteries, particularly in cell phones and in laptop computers. In mid-2006 Sony had to recall 10 million batteries because of a manufacturing defect that caused them to ignite. But the problems are being solved and the quality is getting better.
Particularly for power tools, I would suggest that it would be a good choice right now.
With customers demanding more and more power from their tools, it is becoming more and more difficult to manage the weight associated with the higher-power NiCd batteries. Li-ion is a good compromise.
But, be sure to follow all the manufacturer's recommendations. A Li-ion battery can be dangerous when subjected to abuse.