As mentioned many moons ago... I modified a Dremel rotary tool to
use Bosch batteries. Bosch includes a real charger, and the
batteries last longer per charge. The battery plugs and unplugs
into a wire that goes to the rotary tool. So the weight of the
battery is not felt at the tool. It's like both corded and
cordless, the battery is carried and must rest on something or sit
in my pocket.

Have used it many times. Works great. They rotary tool is
extremely light and easy to handle/control, without the battery
stuck into the case. Much easier to control than using a flex
shaft.

I'm not suggesting the idea is novel concept. Long ago, my dad
stuck a light on the barrel of a rifle. The battery was kept in an
Army belt, with a wire going to a plug in the stock of the rifle.

Any cordless (but wired) tools offered like that? Might not be a
big deal when using a power drill, when you might be concerned
about sudden torque damaging your wrist or arm. But it's great for
a rotary tool.