What is a key characteristic of sealed batteries?

A key characteristic of sealed batteries is that they are designed to not release gases during operation. This is accomplished through a sealed design that prevents the escape of gases such as hydrogen or oxygen, which can occur in traditional flooded batteries during charging and discharging cycles. This sealed nature makes them maintenance-free, as users do not need to periodically fill them with water or attend to electrolyte levels, which is a requirement for flooded lead-acid batteries.

Sealed batteries, often utilizing absorbed glass mat (AGM) or gel technology, also contain their electrolyte in a manner that prevents spillage. As a result, they are less hazardous and are often used in applications where safety, reliability, and low maintenance are priorities.

The other options highlight characteristics associated with different battery types. For instance, the need for regular maintenance and filling with water is typical of flooded lead-acid batteries, not sealed ones. Additionally, the mention of having a liquid electrolyte does not apply to sealed batteries that often use a gel or absorbed glass mat design rather than free-flowing liquid.