With four battery technologies onstage and one waiting in the wings, there's sure to be a battery to suit your needs.
Although all batteries are not created equal, they all have the ability to turn chemical energy into electric current to power electronic devices -- from tiny digital music players to big notebooks. As with the battery in a car, a chemical reaction inside a notebook's battery frees electrons to flow from the positive terminal to the negative terminal, creating enough current to run the device.
That was then
The old-timer of mobile battery technologies is the nickel-cadmium cell (NiCd), once the mainstay of notebook design. Unfortunately, NiCd cells can only carry enough power to run a system for about an hour, and they contain toxic cadmium, which makes them hard to dispose of.
And despite their ability to be recharged about 1,000 times, nickel-cadmium cell batteries also suffer from something called 'memory effects'; over time, they lose the ability to hold a complete charge. Luckily, lighter and more powerful battery designs have surpassed the NiCd, and today, NiCds are used mostly in toys and inexpensive cordless phones. About a decade ago, most notebook makers switched to nickel-metal-hydride batteries (NiMH). Not only can these batteries hold about 40 percent more power, they aren't as susceptible to memory problems as NiCds are, and they are more environmentally friendly. On the downside, you can recharge them only about 200 times versus 400 charge cycles for newer designs.
| Five battery technologies compared | |||
| Chemistry |
Peak watt-hours / no. of recharges |
Problems |
Main use |
| Nickel-cadmium (NiCd) | 80 / 1,000 | Heavy for the power it holds, memory effects, contains toxic elements | Toys, cordless phones |
| Nickel-metal-hydride (NiMH) | 120 / 200 | Moderate weight for power, limited lifespan | Rechargeable batteries, older notebooks, mobile phones |
| Lithium-ion (Li-ion) | 160 / 400 | Hard to manufacture, expensive | Notebooks, handhelds |
| Lithium-ion polymer (Li-poly) | 130 / 400 | Hard to manufacture, expensive | Mobile phones and backup batteries |
| Fuel cell | n/a | Experimental, expensive | Space shuttle, power plants, automotive research |
This is now
Today, the lithium-ion cell (also known as Li-ion), which holds roughly twice the capacity of a nickel-cadmium battery, rules the notebook battery roost. Used on most notebooks, handhelds, and mobile phones, lithium-ion technology can hold a lot of power, but its exotic materials make it expensive. Part of the credit for its success goes to a tiny controller chip embedded in each battery that adjusts how quickly the battery discharges and prevents it from overcharging.
Coming soon
Look for lithium-polymer (Li-poly) technology to make its way into mobile phones, handhelds and notebooks in the near future. Extremely light and malleable, these batteries are capable of providing nearly as much power as lithium-ion cells but can also be shaped to fit into a device's hidden nooks and crannies. For a look at another battery technology, check out the next section on fuel cells.
Dear reader,
Don't get confused by the descriptions above about the flow of electrons to and from the positive and negative electrodes.
A negative electrode is negative because it carries a surplus of negative charge. As electrons are negatively charged, this means that the negative electrode has an excess of electrons.
Similarly, the positive electrode is positive because it has a lack of electrons - and it is the tendancy of the electrons to move in such a way as to balance this out that causes electric current.
In other words, electrons will flow out of the negative electrode into the external circuit (in this case, the laptop's electonics), through this circuit and into the positive electrode.
The place to which the description refers is from the electrode into the electrolyte - the conductive paste that is between the electrodes inside the battery. Electrons move from the electrolyte onto the negative electrode, and from the positive electrode into the electrolyte.
The direction of flow (from the negative to the positive) is called electron current.
However, because our brains like to think in terms of positives, and because the early experimenters with electricity did not realise that the current was being carried by negatively charged particles, they defined current in terms of flow of positively charged particles from the positive to the negative. This is called conventional current.
A way of visualising this in electron flow is the opposing flow of "holes" into which an electron can move. As an electron moves forwards in the direction of electron current, the (effectively positively charged) hole moves backwards - in the direction of conventional current.
The effect is identical - charge is carried around a circuit through charged particles.