Who wants to make an urgent dash to a power outlet to rescue their laptop battery? That’s no fun, especially with everyone working and learning from home these days in various corners of the house that may not have a convenient socket nearby. Luckily, modern laptops are much more efficient than their predecessors. Nowadays, even inexpensive desktop-replacement laptops and some gaming behemoths can last for more than eight hours on a single charge. Ultraportables often endure for 14 hours or more.
Three types of batteries power the laptops you’ll find in service today, nickel cadmium (NiCad), nickel metal hydride (NiMH), and lithium ion (Li-ion), with Li-ion being the most common in newer laptops. Each battery type has a different chemistry for generating a charge and, therefore, different characteristics.
CapacityThe capacity of batteries is measured by power delivered per battery weight, rate of self-discharge, and useful cycles. Power is often measured in watt-hours per kilogram, or Wh/kg. Self-discharge refers to the fact that all batteries lose power when they’re stored. Cycle refers to how many times a battery can be taken from a full charge to a full discharge before the battery can no longer hold power.
The fact that batteries discharge over time is affected by temperature. At higher temperatures, the discharge rate is faster. The general rule to follow is to store them in a cool place and use them at room temperature.
Nickel cadmiumIn tests performed in a lab by Cadex Electronics, Inc., nickel cadmium batteries had a life of 1500 cycles, which means they went from full charge to full discharge 1500 times before giving out. Because of the chemistry of this battery, however, NiCads can suffer from a so-called memory effect.
And like NiCad batteries, if you don’t fully discharge and recharge them periodically, their useful life is reduced. You could potentially get only 175 cycles out of them. On the other hand, they do better than NiCads when you discharge them only a little bit before recharging. Unlike NiCad cells, you increase the number of cycles when you work with your laptop unplugged for just a little while, then plug it in and recharge the batteries. Remember, NiCads like to be fully emptied, NiMH batteries prefer to be only partially drained.
Lithium ionOf the types of batteries mentioned here, lithium ion cells have some powerful advantages. They have an energy density of 150 watt-hours per kilogram. Like NiMHs, Li-ion batteries have no memory effect. That is, they don’t lose the capacity to fully charge if they aren’t fully drained. Left on the shelf, they lose the least power. Their discharge rate, at 10 percent per month, gives them a good storage life (but they must be used within two years of manufacture).
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