I just converted a Dremel 10.8 V rotary tool to use Bosch 10.8 V batteries. I always have the rotary tool immediately in front of me, so the battery will either be worn on a neck strap or be set down near the work. The wires coming from the rotary tool plug into the battery, using a socket taken from another Bosch tool.
That was done because the rotary tool battery charger sucks. Apparently the charger destroyed one of my two battery packs. Also, I have lots of Bosch 10.8 V MAX batteries.
Preliminarily speaking, having the battery connected through a wire to the tool is working great. It's a cutoff tool, so maybe the fact that it is ultra light without an integrated battery is the reason. Or maybe it's just infatuation, wouldn't be the first time. The battery pack can be worn around my neck, hung from a utility belt, or set on a table (the way I'm doing it now).
I suppose eventually battery technology will be light enough that we will reach the point of diminishing returns for lightness, but that hasn't happened yet.