Be careful what you wish for. You might get it. That ancient saying should be etched into the eyelids of battery designers, who are constantly trying to make things smaller with more oomph (or "higher power density", as they call it). It's not entirely their fault, of course -- we want it too.
For most of the history of electronics there have been two types of rechargeable batteries -- lead acid and nickel cadmium. Car batteries and runts. Lead acid is too darn heavy for things without wheels (although Apple put one in its first portable Macintosh, as well as a carrying handle forged from melted-down Saturn V thrust girders -- no coincidence), while nicads have all the stamina of a deflating balloon.
Initially, the only people who cared were policemen with walkie-talkies, but then personal consumer electronics arrived in the shape of the Sony Walkman. A dead battery meant no Dire Straits. Something had to be done...
Nearly 30 years of intensive research into electrochemistry and material science followed and now we have lithium-ion batteries of almost freakish power density. It's too late for Mark Knopfler, but just right for our mobile phones, laptops and digital cameras, all of which need watts by the boatload. Some laptop batteries can supply 25W of power for four hours -- by battery standards, that's like landing on Mars.
Unfortunately, the physics has a sting in the tail. 25W makes things nice and toasty, but if you try to get the same amount of power out in a much shorter time -- because the battery short-circuits, for example -- that toast turns to magma. Lithium-ion batteries are capable of delivering huge amounts of power in a very short time -- in the case of our laptop cells, up to 7kW over a few seconds. The internals of the battery can reach 600°C, with the result that the highly reactive contents blow-torch their way out of the case and into anything in the neighbourhood. Like your lap.
Of course, there are safety features -- very good ones, too, which is why lithium-ion batteries took 20 years to develop. Even so, in the US there were 83 reports of mobile phones exploding over a two-year time period, out of around 170 million phone users. This extrapolates to around one in four million batteries exploding every year. There are probably around two billion batteries in use in mobile phones and laptops, so that's a lot of scorched trousers out there.
Another name for a very small device able to turn its surroundings into glowing embers is 'incendiary bomb': lithium batteries are already thought to be at fault for a fire in a freight aircraft, and it's only a matter of time before something goes on the fritz in the passenger compartment -- accidentally or deliberately. With the border police in various countries already getting a taste for scanning your hard disks on entry, the days of international travel with your laptop may be coming to an end.
But that's not the most serious problem. Lithium ion and its various friends are the only power sources that are light and muscular enough to make sense of electric cars -- and electric cars are the only thing on the planet that might save us from environmental meltdown. If health and safety decides that it's just too risky to strap ourselves into a small box with the ability to instantly vapourise its contents, are we just going to have to walk?
So enjoy the various pictures of burned-out laptops on the Net. Chances are, it won't happen to you, but the end effect may be a lot hotter for all of us. -Rupert Goodwins