Batteries – choice, reliability and legislation
Batteries are essential for many types of electrical equipment and the correct choice is important to avoid early failures. New legislation can drive changes in design with unforeseen consequences. Understanding how to comply with legislation without compromising reliability is a critical issue.
Batteries were originally developed by Alessandro Volta in 1800 and has been the subject of research ever since. Today a wide range of battery types are available all of which have different characteristics that need to be understood in order to choose the most appropriate type.
Main battery types
Batteries can be classified as “primary” or “secondary” types. Primary batteries are fully charged when new but cannot be re-charged after they have discharged. Secondary batteries are “rechargeable” and include nickel / cadmium and lithium ion batteries. The table below lists some of the most commonly used battery types.
| Battery type | Characteristics |
| Zinc – carbon | Low cost primary battery. Lower energy storage capacity than most other types |
| Alkali | Primary battery with higher energy capacity than zinc carbon. Some secondary types have been developed but are not widely available |
| Nickel / cadmium | One of the first rechargeable batteries. Suffers from the “memory effect” but widely used in power tools, emergency lighting, etc. |
| Nickel – metal hydride | Developed as a cadmium-free substitute for nickel / cadmium. A suitable replacement for most conditions but characteristics are not identical |
| Lithium ion | Commonly used rechargeable for laptop PCs, mobile phones, etc. |
| Lithium manganese | Increasingly popular primary battery. Panasonic produces a rechargeable button cell version |
| Lithium thionyl chloride | High storage capacity primary battery used as back-up power storage. Can be attached to PCBs |
| Lithium iron disulphide | High capacity, long life, primary battery |
| Lead acid | One of the earliest rechargeable batteries used in vehicles and for back-up power storage |
| Silver oxide and zinc air | Small primary batteries used for hearing aids |
This is not an exhaustive list of battery types and many others are available so that choosing the optimum type for a new product design can be quite difficult. All batteries are different and so operating temperature, voltage, discharge rate and self-discharge rate all need to be considered. Additional variables must be considered with rechargeable batteries; how many times can they be charged and discharged is important and each type needs a specific type of charger.
Reliability issues
Batteries are remarkably reliable and ERA’s Reliability and Failure Analysis Group is rarely asked to investigate battery failures. All types of rechargeable batteries have a finite life as they can be charged and discharged only a certain number of times but, if this is much less than expected, this usually indicates that battery charging has not been carried out correctly, not that the battery is defective.
Dramatic failures of lithium batteries do occur, however, and ERA has been asked to identify the causes of several “explosions” that have occurred in a range of products. The recent failures of lithium ion batteries made by Sony and used in laptop computers was widely reported in the press. Failures to lithium camera batteries also occur and are reported in letters published in photographic magazines.
Lithium based batteries offer many performance advantages over other types; high capacity, low self-discharge rate and long shelf life being important in most portable electronic products, but lithium is a very reactive metal producing hydrogen gas on contact with water and it also burns readily in air. Lithium batteries are designed to prevent failures but these measures are not always foolproof. ERA’s experience is that “explosions” can occur if batteries are defective – there have been several examples of this – or they are used incorrectly. Overcharging and over-discharging can be dangerous; over-heating and short-circuiting can also lead to failures.
Legislation
In the EU, batteries are covered by Directive 2006/66/EC which replaces 91/157/EEC “on batteries and accumulators and waste batteries and accumulators”. Battery producers, who include manufacturers and importers of equipment that contain batteries, are responsible for financing recycling at end of life. The amended Directive also restricts the use of cadmium and mercury in batteries although there are some exemptions. This Directive was discussed in ERA’s environmental newsletter, RE 4view (issue 30, November 2006).
Other countries outside the EU have also introduced measures that affect batteries. Batteries are outside the scope of the EU-RoHS directive because they are covered by the EU-batteries Directive but they are included in the cope of the so-called “China-RoHS” legislation which requires that they are marked with pollution control symbols. The US Batteries Act of 1996 restricts the use of mercury in batteries so that it is used now only in alkaline and silver oxide button cells. This Act also requires nickel / cadmium batteries to be specifically marked. 13 US and several Canadian States have compulsory collection and recycling programs for batteries.
Further information
ERA’s Reliability and Failure Analysis group has wide experience of electrical product failures including forensic skills to identify the problem and root cause, and design skills to assist in defining remedial action. To find out more call us on +44 (0)1372 367444 or email: info@era.co.uk
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