Hello everyone,
I have a problem with the battery playtime of my Harman Kardon Onyx studio 4.
On max volume it lasts barely 1h30min whereas it used to last at least 3h (it should last a theoretical 8h of playtime on normal volume).
Thinking that the battery life had ended, I replaced it with a new one and charged it as recommended but the problem persisted.
I replaced the battery with another new one thinking that the other may be defective but the problem is the same.
When plugged to a wall outlet, the speaker works for as many hours as needed, it charges as well, so I don't think there's a problem in the power input. The battery lasts for more than 3 hours on normal volume.
I have another same speaker but newer and the battery lasts for more than 3h on max volume.
What could be the problem? Could it be the charging circuit ?
Many thanks!

 

It could be any number of things.
These little Speakers are built to satisfy a "Price-Point" so
the Engineering and Quality-Control is sometimes limited.
I'm genuinely surprised to hear that they withstand full volume for hours-on-end.

You can take the old and the new speakers apart and compare the
Battery-Voltages while they are being charged.
Unfortunately you'll spend more Money and Time trying to fix it,
than the actual cost of a new one,
that is,
if you are ultimately successful at finding the problem and fixing it.

An extension-cord is cheaper and more reliable.
.
.
.

 

I think the newer one uses a more efficient class-D audio amplifier but the old one used a class-AB amplifier that wastes more current. The newer battery also might have a higher rated and actual capacity than the old one.

 

The ultimate proof would be if you measure the current it draws from the battery. If one is very different from the other, there you have it.
Also, maybe it would be useful to maintain measurements of the battery voltage as well, so you can compare the capacity of one against the other.
Edit: other than that, I don't see any other more useful tests.