Some kind of Solanum, I would say, perhaps S americanum.

Floral, could it possibly also be a Physalis species? Is there something diagnostic that makes you think it's S. americanum? Given all the similarity, and variation in the leaves of both genera, maybe waiting to see a flower might be advisable?

Could be. But I was thinking of likely common bird spread weeds, given that it's on a balcony. A bit more info. on the location would be useful. Are there gardens growing ground cherries or similar nearby?