There's never a stupid question.
I don't have a
joyetech Cuboid, but from pictures (see above), it appears that it is a two battery mod, and that one battery is inserted positive down while the second battery is inserted positive up.
I'm assuming that you placed electrical tape around the positive end of the battery to help identify it as the positive end. And now you have found out that the tape is just thick enough to change the girth (diameter) of the battery enough so now the battery is stuck. Marking the positive end with a magic marker, in hindsight, would have been a wiser idea.
Unless someone else comes up with a better plan, you will have to find some type of "tool" to slide between the battery and the battery sled in the mod to tease or pry the battery out. This will likely damage the protective plastic covering of the battery, known as the insulating wrap. DO NOT USE THIS BATTERY if the protective wrap is damaged in any way, its there for an important reason. Either have the battery re-wrapped or use a new battery in its place.
Sorry for not having a better answer to your problem. However, I felt it important for you to not use a battery with a damaged wrapper.
A tool that has a sort of "hook" might be what you need, like what some Swiss Army Knives have. Not sure if there is enough room to slide this tool into the battery chamber.

Or, a seafood pick might work. Again, you don't have much room to slide between the battery and sled.

