What's the best battery for laptops(2)?Batteries for laptop have a unique challenge because they must be small and lightweight. In fact, the laptop battery should be invisible to the user and deliver enough power to last for a five-hour flight from Toronto to Vancouver. In reality, a typical laptop battery .

What then is the best battery for a laptop? The choices are limited. The NiCd has virtually disappeared from the mobile computer scene and the NiMH is loosing steam, paving the way for the Li-ion. Eventually, very slim geometry will also demand thin batteries, and this is possible with the prismatic Li-ion polymer.

A fully charged Li-ion battery that is stored at 45°C suffers a capacity loss from 100 percent to about 70 percent in as little as six months. If this condition persists, the capacity degrades further to 50 percent in twelve months. In reality, the battery in a laptop is exposed to elevated temperatures just during use and the battery is in a full charge state only part of the time. But leaving the laptop in a parked car under the hot sun will aggravate the situation.

For mixed battery and utility power use, the Li-ion system is a better choice. If a fully charged Li-ion is placed on charge, no charge current is applied. The battery only receives a recharge once the terminal voltage has dropped to a set threshold. Neither is there a concern if the device is connected to fixed power for long periods of time. No overcharge can occur and there is no memory to worry about.

NiMH is the preferred choice for a user who runs the laptop mostly on fixed power and removes the battery when not needed. This way, the battery is only engaged if the device is used in portable mode. The NiMH battery can thus be kept fresh while sitting on the shelf. NiMH ages well if kept cool and only partially charged.

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