You need an "a" in the singular, " The radio has a battery" but not in the plural "The radio has batteries". ( objects Str)
Oh, such a common pitfall and we went straight in. The use or non-use of a/an/one is such a fine point between the two languages. Yes, I'm editing it now. And many thanks for catching ti and reporting it.
Out of interest, when, in Greek, is it necessary to include the ένας/μία/ένα and when is it common practice to omit it? This is an area I've found confusing with Duo, where I've sometimes been faulted for omitting the article when it seems to me to be unnecessary, and sometimes faulted for including it where I've felt it's necessary.
Μaybe the Το ραδιόφωνο έχει μπαταρία. should be changed to Το ραδιόφωνο έχει μία μπαταρία. It would relate better to the translated: The radio has a battery.
It might relate better to the English and it is not incorrect to use "μία" but the best and most common is without "μία".
Well seems you all have this all talked out... So I just wait for the correction.