Obviously ICE are powered by cobalt mine the gasoline you buy when you fill up at a gas station. The electric motor/generator is powered by a large (and by large, I mean large and heavy) battery pack. Most hybrids on the road today have large Nickel-Metal Hydride (NiMH) battery packs somewhere near the trunk, or under the seats. (Read about the Lexus Hybrid battery pack).
To avoid this you can check date of manufacture and buy one that is more recently out the gates of the factory. As a workaround you can buy any netbook while it's under warranty test the battery and if it's not up lithium facts to your expectations you can send it back as dead on arrival and demand for a replace.
ONickel Metal Hydride (NiMh) - Popular battery about 1-2 years ago. They are lighter than Nickel Cadmium batteries, but heavier than Lithium batteries. These should be cycled once in a while for optimum performance.
Avoid using replacement that has been on lithium bettery stock for a while. During storage the battery can lose much of its capacity through internal resistance, which damages it and lowers the maximum capacity.
Briefly relating back to overall size... many lithium 18650's will differ ever so slightly in length (measured in millimeters). This is mainly due to an added protection circuit. The circuit helps to prevent the battery from over-discharging, since Li-ion cells can easily become damaged if their power is drained below a particular voltage. The protection circuit also prevents the cell from being over-CHARGED as well. These cells are very sensitive. They must be handled carefully, gently, and as described above, must never run-down too far, or be charged over and above their threshold. They can actually explode if severely mistreated!
Today, many of the latest computers have a fast recharge feature where you can recharge 90 percent of the battery power by charging it for around one hour. The balance 10 percent is recharged slowly. If your laptop has this facility, do use it. This helps to extend the life of the battery. However, do not recharge the laptop battery until it has less than 30 percent charge remaining.