There are three types of weed eaters: gas, electric and battery-powered. Gas weed eaters are the heaviest of the three types, but are the most convenient for medium to large lawns. Gas weed eaters also last longer than electric or battery-powered weed eaters, so if you plan to use the weed eater often, a gas weed eater is the better deal.
Gas weed eaters are best for larger lawns. A gas weed eater is heavier than an electric or battery-powered weed eater, but allows the user the freedom to move around the lawn and not have to worry about cords or stopping to charge the battery. Some gas weed eaters also have optional attachments, such as an edger or a tree saw attachment. Most gas weed eaters have two-stroke engines, which means that the user must mix two-cycle oil with the gas. Some weed eaters now have four-cycle engines: these use straight gas.
Electric weed eaters are lighter than gas weed eaters. They plug into an outlet, and users are limited to the length of the cord. Electric weed eaters are not as powerful as gas weed eaters, and are meant to be used for small yards with few areas to weed eat. An electric weed eater will not cut thick weeds.
A battery-powered weed eater uses an electric motor, but instead of a cord, it runs on battery power. A battery-powered weed eater is not as powerful as an electric weed eater and can only be used for light-duty weed eating. The battery must be charged each time you use the tool, and sometimes, depending on the size of the yard, might have to be charged more than once to complete the entire yard. Benefits of a battery-powered weed eater include being able to work on a larger yard (no cord restriction) and the convenience of not having to mix fuel and oil.