A Better Gauge on Battery Life

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The problem gets worse as the battery ages and, as the battery is depleted, voltage drops more quickly. With conventional gauges, this could trigger the phone to shut down when there is still quite a bit of energy left. Indeed, much of the perceived loss in battery life in older phones is actually just a problem with the battery gauge. "You can lose 30 percent of the energy in a battery simply because the device shuts itself down too early," says Richard DelRossi, an engineer at TI. He says that the new, more accurate battery gauge could increase the usable battery capacity by as much as 50 to 100 percent, depending on the power-management strategy.

Other phone and chip makers are also developing better battery gauges. Approaches taken by Motorola, based in Schaumburg, IL, and PowerPrecise, a chip maker based in Herndon, VA, that's funded by Intel, combine voltage data with current measurements to determine how much energy has been used. Subtracting the amount of energy used can give a good idea of how much is left, as long as it's known how much energy was there to start with. But the capacity of the battery, as with the voltage, depends on certain conditions, such as temperature, battery age, and power demand. To adjust for these factors, these systems can refer to models of battery behavior based on earlier tests to guess how these conditions will affect the battery's overall capacity. Such a system gives a much more accurate gauge of battery charge than do voltage measurements alone, says Jerry Hallmark, who heads Motorola's research on energy consumption in mobile devices.