Battery Boosters

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Juice Up Your Laptop

If you need 5, 8, or even 12 hours of computing time untethered to an electrical outlet, invest in a slim battery slice that rides beneath your notebook and greatly extends your laptop's running time.

These notebook battery extenders contain anywhere from 80 watt-hours to 300 watt-hours of additional juice, courtesy of lithium ion or lithium polymer cells. Depending on how much power your machine consumes, adding a battery slice to your notebook's internal battery could give you 3 to 10 hours of extra running time without a recharge. The slab plugs into your laptop's power port.

We tested Valence's $250 N-Charge VNC-130 and Hi-Capacity's $170 PowerPlus 60. The N-Charge weighs 3 pounds and provides 120 to 130 watt-hours of power. On a Dell Inspiron 710m, that translated into an extra 5 hours, 49 minutes of running time; and on an ultralight model, the Sharp PC-M4000, we got an extension of 9 hours, 8 minutes. The PowerPlus 60 weighs 1.2 pounds and provides 60 watt-hours of juice. In our tests, it powered the Dell laptop for an extra 2 hours, 40 minutes, and the Sharp model for an additional 4 hours, 33 minutes. The battery you select should depend on the running time you need and the extra weight you can carry.