If Indians and the Chinese buy more cell phones than anyone else in the world, that also makes them among the world’s largest consumers of rechargeable batteries. As more desktop computers are replaced by laptops, there is increasing need for such batteries. And with film cameras giving way to digital ones, still more batteries will be needed. Quite simply, all devices for mobility and convenience need compact sources of power and, for the foreseeable future, this will be provided by rechargeable batteries. The more compact these devices become, the smaller their batteries need to be.

The lightest known metal, lithium, was first proposed for use in batteries almost a century ago but the inherent instability of these batteries meant that they were highly prone to fire. Work started again in the 1970s but it took 20 years before reasonably safe and rechargeable lithium batteries hit the market. Today, there are lithium batteries that are used for devices that have long life, like cardiac pacemakers. Another type of lithium battery (the more common “button” cell) is widely used for devices like clocks and digital cameras. The next major innovation came with the use of lithium ion, instead of lithium, for batteries. This allowed the mass production of much safer batteries which are well suited to uses in devices like cell phones and laptops.

Lithium ion batteries can be made very compact and improvements (e.g. using polymers) will allow them to become slimmer and smaller. They take a relatively long time to charge (typically one-two hours) but will then store the charge without much loss for periods as long as a few months. A major drawback is that lithium ion batteries start degrading almost as soon as they are manufactured: whether used or not, they will need replacement within about two-three years. Fortunately, that matches reasonably well with the average replacement life of a cell phone or camera.

“Safety” is a relative term and manufacturers measure it in terms of the probability of a single battery failing (or catching fire). They estimate the average failure time (the Mean Time Between Failures, or MTBF) by putting a batch of batteries through extended tests and observing when the breakdowns occur. Safety is also measured in terms of numbers: while one battery may be considered safe, a crate full of batteries may not. For example, airline regulations allow a device with a single lithium battery to be carried on board but prohibit the shipment of lithium batteries as cargo.

The $5 billion world market for lithium ion batteries is dominated by East Asian manufacturers. Japan was the world’s largest supplier with 80 per cent of the market, but there are now major manufacturers in China and South Korea as well. The large Japanese manufacturer that was also the pioneer in making lithium ion batteries is, ironically, the one that recently had to recall over 10 million batteries supplied to laptop manufacturers because of the risk of fire. This kind of occurrence is both unfortunate for the buyer of the equipment and very expensive for the manufacturer.

However, this is the price that will have to be paid. Manufacturers are under increasing pressure to make batteries smaller and to last longer. This makes the design and manufacturing margins tighter and tighter and inevitably the chances of weaknesses will increase.

Rechargeable batteries are inherently toxic and need to operate within strict limits for both safety and long life. For example, if a lithium battery is short-circuited, it can generate enough heat to explode; a lithium battery should never be fully discharged or it will lose its ability to store charge. So, such batteries have added circuitry designed to prevent unwanted conditions from developing. But, within the battery itself, only a thin polymer membrane is used to separate the positive and negative poles and this can become a weak point. Not much can be done to increase the reliability here because there are competing pressures to reduce the size and thickness further.

Hundreds of millions of lithium and lithium ion batteries are in use today and tens of millions are being produced by major manufacturers each year. No one has recently been injured through such batteries catching fire. But there is undoubtedly a higher risk of that happening today than before.

The increased risk, however, has had no effect on the demand for smaller and more powerful rechargeable batteries. The buyer of a cell phone or a digital camera rarely considers the risk from fire or explosion of the battery. In fact, new applications are increasing and even electric-petrol hybrid cars are expected to start using lithium ion batteries in the future.

There are other many new battery technologies being developed. One invention reduces the charging time for a battery to a few minutes; others increase the life and the storage capacity. But it will be some years before any of these technologies reaches the maturity level that is required for large-scale manufacture. Until then, we will live with the risk, cheerfully and obliviously in most cases.

Dr Mathai Joseph is executive director, Tata Research Development and Design Centre, Pune.He earlier was chairperson of software engineering at the University of Warwick for 12 years and a visiting professor at Carnegie-Mellon University and at Eindhoven University of Technology. This is a monthly column.