A cordless trimmer is an electrically powered landscaping device with a slightly similar design principle to a chainsaw, though the blades reciprocated in a back-and-forth motion, rather than a circular motion on an oblong track. These are primarily used for smaller branches, small-scale tree trimming, trimming hedges and bushes, that sort of thing, where a chainsaw is an unnecessary danger and overpowered.
Cordless trimmers usually utilize a lithium-ion battery, which is the same basic technology used by handheld devices, tablets, smartphones, and other rechargeable electronics. A large difference between these batteries and those in phones is entirely based on the fact that there’s usually a transformer, and a bank of capacitors to yield a larger sustained electrical signal to drive the motor.
Many companies produce these, including many respected and popular brands, and these batteries are usually somewhat universally compatible across the board. This is a somewhat dangerous tool, albeit not as dangerous as a chainsaw, and caution should be exercised at all times. Minors should never use these tools without supervision, without excuse.
On average, these devices get about six hours of use between charges, with some being a little lesson something more, depending on the quality of the battery in the tool in question.