"The basic issue is that the density of the power we are dealing with [in laptops] is quite hazardous," said Dean McCarron, an analyst at Mercury Research (Cave Creek, Ariz.).

"We've created a beast," said Jim Templeton, co-founder of power-management IC startup Zilker Labs Inc. (Austin, Texas). "Notebooks have rising thermal envelopes, more localized hot spots and limited cost budgets to solve these rising power-management challenges."

Engineers, testers and other industry experts said last week that quality control problems at battery maker Sony's production lines, along with a lack of robust battery cell materials, were key contributors to the largest consumer recall in history. But design engineers said the proliferation of smaller, graphics-intensive mobile devices is raising more-fundamental issues.

"It's a matter of how systems are architected," said Bodo Arlt, publisher of Bodo's Power Systems magazine in Germany. "You need to know how much energy the computer extracts from the battery, and how a system is designed to manage the current flow that generates heat inside the battery. Knowing the limitation at the critical temperature is important."

Added Arlt, "Graphics-intensive applications such as computer games could create a huge stress on computers, resulting in a demand for extreme power. Once [a computer] overheats, it can start burning."

Overtemperature circuitry
Robert Dobkin, CTO and vice president of engineering at Linear Technology Corp., said it's a mistake to focus on the placement of battery packs relative to microprocessors and graphics processors on a laptop motherboard. Overtemperature circuitry prevents today's battery packs from charging at temperatures greater than 45°C to 50°C, Dobkin said. In his view, the overheating from processor power dissipation could lead to system problems, but not the catastrophic fires seen in some laptop failures.

Instead, fire danger relates to battery chemistry in poorly designed batteries, or in the overvoltage protection used in integrated battery packs, he said. Simple Li-ion designs lack the ability to handle overvoltage, Dobkin said, so the battery manufacturer or system OEMs must add it. Sony and other large battery makers integrate a voltage protector into the pack, he said.

McCarron of Mercury Research said most consumers don't realize how much power is packed into lithium-ion batteries--a notebook battery can hold as much as 100 watt-hours of energy--and how sensitive the chemistry is to disruptions.

In this case, he said, Dell may have been guilty of design flaws that created hot spots within the notebook case. But McCarron said the recall stemmed from quality control problems at Sony.

A testing lab official agreed. "It is basically a quality [control] problem in the cells," said John Drengenberg, an electrical engineer and manager of consumer affairs for Underwriter Laboratories Inc. (Northbrook, Ill.). "Power density is increasing dramatically," he added, while battery cell materials have failed to keep pace.

Reports last week suggested that faulty crimping on a Sony production line may have introduced metal contamination to the cathodes of the affected battery packs, leading to a half-dozen or more reported fires. "If it were a design problem at Dell, we would have had many more [fire] problems," said McCarron.