Bluetooth speakers: Flashy, loud, mobile

In the open-air swimming pool, at a barbecue in the park or at a picnic in the garden: Bluetooth speakers play music from your smartphone or tablet even where there is no other music. The music reaches the speaker via Bluetooth short-range radio. They present it louder and more sonorous than the mobile phone. But which speaker sounds best? How long does the battery last? Which is light and easy to transport? The test of 18 speakers reveals the differences.