(Febuary 2004) Batteries Canít Keep Up
According to a story in the Washington Post on January 11, 2004 p. F07, the reporter claimed that Lithium-ion batteries are susceptable to aging to the frustration of product owners. It is true that Lithium-ion batteries usually have an unknown or undisclosed shelf life, but the total window of performance starts with the design selections and quality control of the manufacturer. Those cells which use the best combination of materials and construction can be safer and have longer shelf and cycle life than cells produced by low cost manufacturers.
A batterey in BDs first Sony digital camera has underlying quality in the state of charge reporting which has allowed us to use it for over 5 years, and it is still going. Sony knew how to alert the camera owner to the state of charge, limiting the number of times the battery had to be recharged and producing longer life. On the other end of the spectrum is the Canon S30 digital camera also owned by BD. The state of charge indicator shows an icon alert only one snapshot before the battery is fully discharged. Such poor charge status requires that every time we get a chance, we put the battery back on charge to top it off. Less than complete or deep discharge cycles are not as damaging as full recharge cycles, but leaving the cells in the charger to remain at full Voltage which is usually about 4.2 Volts contributes to shorter battery life. Any knowledgeable engineer will tell you that the higher the end charge Voltage, and the longer it remains at that level, the shorter the cycle and shelf life of the cell will be. That is one reason that NASA uses Lithium-ion profiles with maximum Voltages even below 4.0 Volts when considering orbital applications. Also, check the chargers built by Linear Technology for backup applications where long life is important. Instead of charging to 4.2 Volts, the chip only charges to 4.0 Volts.The bottom line here is that the userís battery life is limited by the manufacturerís choice of max Voltage and whether the product allows for proper charging regimens.
The Postís story then with its comment, ďThere isnít much that users can do to make the batteries last longer.Ē misses the opportunities for consumers. Buyers need to make choices from product reviews which indicate which are found to give the safest and longest performance. Then too, buyers need to know which products have battery management which leads to proper performance. If buying habits gravitated to those products which provided the best battery performance, manufacturers looking at the lineup of more profitable market leaders might take a greater concern for the battery and battery management quality in thier product.
Not only do expensive battery systems need to have accurate state of charge infomation, they also need state of health information. When we pay over $100 for a notebook battery replacement, we should expect charge reporting which can be had for less than $5 ..
Even the U.S. military suppliiers gave troops on the ground less than suitable battery operated radios which had no battery state of charge or health for operation in Iraqi Freedom. The bet-your-life-on-the-battery-charge led ground troops to constantly replace not yet discharged batteries, which almost depleted supplies during combat.(See BD #89, p.2)
The bottom line is that batteries have constraints and limitations which go beyond just the manufacturing regimen. Designers who integrate battery information into the product allow for maximum useability.
(Oct 2003) Batteries Look Forward to Longer Lives
Longer battery life is implicitly understood to require greater energy density. On a more practical side, National Semiconductor and ARM are working together form the standpoint of making more power efficient systems by adjusting performance and power consumption in portable chips. National embraces its PowerWise technology and ARM its Intelligent Energy Manager solution. Improvements will be made in many steps with eventual targets form 25% to 400%. Initial algorithms are targeted to provide 25% to 75% efficiency imporvements for digital baseband. ARM will license the core and National will build the external power supply chips.
Ref: Wireless Systems Design, Jan/Feb 2003