As we heard on Monday, batteries don't last long enough for today's laptop users. Yesterday we looked at the prospects for fuel cells, but you won't be able to buy those for a year or two.

In the short term, the only option for really extended battery life is to buy spares. But even this option can be a dangerous one. When it comes to lithium ion batteries, users who choose the cheapest option can literally get burned, says Sara Bradford, an analyst at Frost & Sullivan.

Lithium ion batteries are generally safe but require strict levels of quality control in the manufacturing process. The factories making knockoff batteries don't always meet those standards. "It's the replacement batteries where the problems come in," says Bradford.

"Under certain conditions, lithium ion batteries can go into a thermal runaway event where they can burn at up to 800 degrees Celsius," says Joe Lamoreux, vice president and general manager at Valence. His company makes an external lithium ion polymer battery pack for notebooks that replaces the traditional cobalt oxide with a more benign phosphate technology that he says eliminates the risk. The trade-off: the batteries are more expensive, and power density is about 20 percent lower than cobalt-based lithium ion.

Improper use can also trigger battery explosions, says Donald Sadoway, a battery expert and professor of materials engineering at MIT. Batteries require a specific charging current. Cheap knockoff batteries may look the same but require a lower current charge. When the user puts it on the charger, "boom, the thing blows up. Why? Because the battery was made more cheaply and maybe should have charged at a lower rate," Sadoway says. The same result can occur if a different power brick is attached to the wrong device - a mistake that's all too easy to make, since many power sources for different devices are plug-compatible. "If you have different power bricks, label them and don't mix them," he says.

Lithium ion batteries are also more likely to explode when high current is drawn, says Sadoway. "If you want to be reckless, draw high current and charge the battery at a very high rate," he says. But that's a design consideration for device manufacturers that's out of the user's hands.

Exploding the myths
Stories of batteries actually exploding have circulated widely, notably in connection with fake batteries for Noklia phones. However, most tales are exaggerated, says Kurt Kelty, director of business development at Panasonic Energy Solutions Lab. In some cases, the heat and pressure created by the runaway chemical reaction can cause the casing to burst open. "What it really means is some smoke is given off," he says. "What happened was there was a thermal event inside the case that caused the temperature to rise and the pressure to rise to the point where it burst the case. The innards are exposed to oxygen and moisture in the air that creates fumes. The consumer sees the fissure and concludes that it exploded."

But the batteries can leak and damage equipment. "There is really a safety issue right now with batteries, specifically some of the ones coming out of China," Kelty says.

Given the cost of mobile computing equipment and the fact that prices of lithium ion batteries continue to decline, the best course of action today may be to stick with name-brand replacements. "Take the financial hit, buy the brand name, the OEM-recommended. If you try to cut costs, you're playing with safety," Sadoway says.

Stretching battery life
A laptop battery should last two to three years, but many users get far less. Here are six tips for getting more out of the lithium ion batteries used in most mobile computing devices:

  • Avoid low-cost knockoff batteries. These can overheat and explode when in use or in a charger. Buy the brand recommended by the manufacturer.

  • Always use the recommended charging unit and battery. A charger that provides too high a current can destroy the battery and cause it to burst. Since different power supply cords can be plug-compatible, clearly label power supply bricks to avoid mix-ups.

  • Turn off a laptop when not in use or at the end of the day when in a docking station.

  • Store batteries at 40 percent charge in a cool place. Putting them in the refrigerator (but not the freezer) can preserve battery life.

  • Stop charging immediately if the battery gets hot. "Cooking" kills batteries.

  • Don't allow the battery to fully discharge before recharging, including secondary or stored batteries.