These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
If a GBA is disconnected, the game freezes for a while before returning to the title screen if the controller is not reconnected. This only allows enough time for the event of the cable accidentally being unplugged. If the batteries in your GBA died... well, you better hope you saved recently. (This is of course true of GBA games, but still...)
Worse yet, the design of the GBA SP and the GBA-GCN cable combined means you can't have an SP plugged in with an AC adapter at the same time you have it connected to the GCN.)