Line powered vs. battery powered
What is the significance of line powered or battery powered?
Battery power is safe and more convenient. But in the “old days,” batteries developed a bad reputation for unreliability and rapid drain. Modern conservation techniques in well-designed equipment have eliminated these shortcomings, making battery-powered units more portable and, of course, not dependent on site power, hence more amenable to field work and construction environments. They also provide a much better regulated power source, free from the effects of transients and other line disturbances. Furthermore, as a self-contained power source, they can be designed so as to be well within safety parameters, which is difficult to guarantee with line power that is connected to the North American grid!
A common misconception is that line power somehow provides a “better” (i.e. more robust) test. The only thing that all that extra power might get you is arc flash! It does NOT provide a more reliable test.
The only disadvantage that batteries do have is that they eventually go dead. This leaves battery power open to “human error.” Dual-powered units, both line and battery operated, therefore offer the best of all worlds. To paraphrase a former light heavyweight champion, Tommy Loughran, “Use battery power when you can, line power when you must.”