I do not think that your speaker is defective. It may be just the way that the charging indicator has been set up.
Also the User manual states that it may take up to 4 hours to fully charge, the first time that you go to charge it.
I do not know your particular speaker but with some devices the charging light is only on when the unit is actually charging. If the unit has been fully charged and then you go to charge it again the light will initially come on as if it going to charge but then will switch off as the charging circuitry in the device detects that the battery does not need to be charged further.
Try playing the speaker for a while, say an hour or two. The specifications state that it is supposed to be able to play on batteries for approximately 6 hours, so playing it for this long should deplete the battery at least by a third, depending on other factors like volume setting etc. Then try charging it again and see if the red charging light comes on and that it takes a while to charge and then it goes out. Then try plugging it in to the power outlet again and see if it exhibits the same as before, i.e. the charging light blinks and goes out. Is so then it is just the way that they have set up the charging indicator and all should be OK.