"I want to swim."
Translation:Jag vill bada.
The difference is clear to native speakers, but it's something learners often struggle with. In this case it would be Jag vill ha båda since båda is not a verb, but I would still hear a clear difference between bada and båda. You'll hear it too with practice.
(to be fair, Swedes may sometimes have trouble distinguishing the a/å as said by speakers of a very different dialect)