Indeed, despite growing demand for PDAs, handheld PCs, and other mobile devices, users often prefer notebooks' keyboards and screen sizes when crunching numbers, checking email, or preparing PowerPoint presentations. The challenge for OEMs has been to boost notebook battery lives while packing the machines with increasingly power-hungry CPUs and graphics processors.

The ultimate goal? To offer the same capabilities that high-powered, battleship desktops offer in a notebook form factor that can run on battery power alone during an entire workday or transcontinental plane ride. Unfortunately, the gap remains between ultra-high performance, power-draining processing power, and long notebook battery lives.

"It's a battle between end user wants for better battery life and improvements in technology that sometimes require more power," says Howard Locker, chief architect for desktop and mobile development at IBM's personal-computing division. "Battery life is also a trade-off between weight and size. You can put a bigger battery in a laptop to get more battery life, but it will weigh more." Notebook battery life is largely taxed by the applications running at a given time and the power of the CPUs, graphics processors, and other components, which must be scaled down to reduce power consumption. "For a longer battery life, a trade-off in performance is thus necessary. It might take a little longer to do things, but if something takes four seconds instead of two seconds but your battery lasts another 45 minutes, then that is a good trade-off," Locker says. "[Designing] intelligent power management by detuning functions and performances that are not needed is critical."

So which notebooks on the market offer the longest battery lives? The answer varies according to many performance variables and form-factor preferences, but Tablet PCs from Electrovaya (www.electrovaya.com; 905/855-4610) and notebooks from IBM (www.ibm.com; 888/839-9289) stand out, says Rob Enderle, an analyst with the Enderle Group.

"In Tablets the Electrovaya Scribbler is the clear winner with nine hours of battery life, but of course you would kind of expect this given Electrovaya is known for its work in batteries, not computers," Enderle says. "The IBM T Series, with its large battery, used to be the segment leader with around six hours of battery life."

So what are Electrovaya's and IBM's secret sauces? "The Electrovaya uses a special high-capacity battery, and IBM's product has a combination of a large battery and a system tuned for battery life as opposed to performance," Enderle says. "The Electrovaya also has a special high-capacity battery that is unique—or at least for now."

So what are the trade-offs involved? "Both products are slow to use, particularly if you run a suite of virus, antispam, and anti-spyware offerings," Enderle says. "However, once the applications are up and running, the performance hit doesn't seem as bad, and many users can get used to it."

Several components are responsible for the performance hit vs. long battery life in the IBM T Series and Electrovaya offerings. "What is causing the performance hit is slower moving drives, which may at times actually spin nearly all the way down between reads, processors working at a fraction of their potential on battery life, dimmer screens, and lower power fans," Enderle says.

Electrovaya largely attributes the Scribbler's long battery life to its patented LiIon, 75 watt-hour battery. The SC2100 also features a 1.3GHz Intel Centrino processor, a 12.1-inch display, 802.11g wireless capabilities, and an 80GB hard drive and weighs in at 3.5 pounds.

IBM's ThinkPad T43, introduced last month and available in April, weighs 4.5 pounds and is also equipped with an Intel Centrino processor that supports up to 2GB of DDR2 system memory. According to IBM, the new T43 can offer up to eight hours of battery life while running office applications, including Internet connectivity with an 802.11 connection.

HP (www.hp.com; 800/752-0900) this month attempted to shake up the battery life sector with the launch of the HP Compaq 6220/6230 notebook series that the company says can offer more than nine hours of battery life when a travel battery, which is sold separately, is added. The notebook's form factor enables the travel battery to be attached directly to the notebook so that it is simultaneously operable with the integrated battery. The notebook series, which offers Centrino CPU clock speeds up to 2.13GHz and a memory capacity of up to 2.048GHz, weighs in at 5.99 pounds when the travel battery is attached.

In addition to the Intel Centrino processor that offers SpeedStep power-saving controls and Intel's Display Power Saving technology for the screen—which represents the most significant power-draining component—HP also says its patented NIC technology helps to lower power consumption on a BIOS system level.

Nine hours is also a realistic benchmark for the HP Compaq 6220/6230 notebook series when running typical applications, such as accessing the Web and checking email with the Centrino chipset's 802.11 capabilities, using a word processor or other applications, the company says. "Nine hours is a realistic test of what you would experience while sitting in a conference room in a, God forbid, nine-hour meeting," says Herman de Hoop, a worldwide technical marketing manager for HP.

ASUS (www.asus.com; 888/678-3688) also represents an OEM with a consistent notebook offering that at least keeps the vendor in the battery longevity notebook race. The company also relies on Intel's Centrino to regulate its latest M3Np notebook's power-saving features at clock speeds of 1.30GHz to 1.70GHz. With ASUS' Power4 Gear power-consumption technology, the company maintains the M3Np can operate more than five hours. The M3Np weighs about 5 pounds.

So what is in store for next-generation long-battery life notebooks? OEMs will likely continue to rely on power-saving capabilities of CPUs, as well as BIOS and other system tweaks to reduce notebook power consumption in future models, but no breakthroughs in battery technologies are in store for the near term. It will likely be several years before battery lives extend beyond 10 hours, which will probably involve replacing power-hungry LCDs with new display types, Locker says.

"I don't see battery life [extending to] up and beyond 10 hours [in the near future]. Inventing a new technology to replace the panels with OLEDs, for example, would do it, but that is four to five years out," Locker says. "However, [OLEDs] will also probably represent the next breakthrough on a system level.