Portable computer power sources

The designers of any portable computer face a dilemma when choosing the power source for their product. The product can be either smaller and lighter than the competition-and possibly suffer from shorter run-time-or it may have superior run-time at the expense of added weight and volume. The balance between these options is a delicate one that impacts product acceptance and ultimately the manufacturer's revenue stream. Of course a high energy density power source represents only half of the run-time equation. The use of lower power hardware to achieve a given level of functionality can have an equally differentiating effect; and much work is currently underway to improve hardware power efficiency (Fadel, 1993). As levels of circuit integration increase emphasis upon power reduction is critical to achieve reliable operation at a reasonable temperature without some form of active cooling. These diametrically opposed design requirements, small size and light weight versus longer run-time, are set against the backdrop of a quickly changing electronics industry and a battery industry that is inherently slower to develop new products