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A magnetic wall detector operates without any batteries since it uses a rare-earth magnet (or magnets). It doesn't actually detect studs but instead locates the nails or screws attached to the wood.
It's a little more time consuming to operate since you're hunting for metal fasteners and doesn't work so well on the walls of older buildings where a deeper scan is needed.
Conversely, an electronic wall detector includes electronic components with the ability to use actual sensors to assist you in discovering the precise location of studs.
Moreover, such electronic devices come with LED lights and audible tones to inform you the moment the edge of a stud is detected. Their biggest negative is that they require a 9-volt (or AA) battery which can provide poor results if not regularly replaced.
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