9V battery with USB get very Hot

Thread Starter


Joined Jun 14, 2018
Hello everyone,
Please see attached circuit image for the following problem.

In order to prevent batteries to get hot, I have to either disconnect the USB cable or the T1 and T2 connection to PWM. USB cable is not connected to a power outlet.

Users can’t open the case to connect or disconnect the USB cable or T1 and T2. Therefore the circuit should work as-is without batteries get hot.

I use a 9v battery with USB to avoided charging PCB. Plus I can faster assembly the charging circuit. If you suggest changing the batteries, I would appreciate also give me a charging circuit.

Thank you very much for your help.



Joined Jan 18, 2008
Your drawing is too unclear to read. It looks like you are using the batteries as some sort of pass through.

What are T1 and T2 connected to? How is the USB connected? Is there a common ground (e.g., at the USB)? That could result in a short across at least one battery. No wonder it gets hot.

Suggestion: Post a clear diagram showing have every connection is made.

Audioguru again

Joined Oct 21, 2019
You should post a link to a sales sheet or datasheet of the 9V batteries. I think they have a charging circuit inside them and a USB jack. If the negative USB terminal connects to the battery negative output then connecting their USB jacks together makes the batteries so that they cannot be connected in series.

Thread Starter


Joined Jun 14, 2018
Thank you to both of you for your replies, T1, and T2 are batteries Terminals.
But Audioguru, you were right, the USB negative is connected to the battery negative pole. I didn't know that; the series circuit is getting short and the batteries getting hot for this reason.

I think the solution to this problem is: to charge the batteries from the separate charing PCB connected to batteries poles.
Thanks a lot for both of your help.