December 2004

Better Battery Gauge

By Technology Review

Your laptop's battery gauge says you have an hour of computing time left, but don't count on it. The older a lithium-ion laptop battery, the less energy it can typically store -- a variation that can throw off the accuracy of conventional battery gauges by more than 50 percent. This winter, Texas Instruments plans to introduce an inexpensive "gas gauge" chip that not only takes into account a battery's original capacity but also measures its impedance -- the resistance to electrical current caused by age, frequent use, and other factors. Built into the chip are mathematical models of lithium-ion chemistry that use impedance measurements to calculate how much a battery has degraded and adjust predictions of remaining charge accordingly.