Could overvolting the USB port on a laptop cause battery drain issues?

So yesterday I was working on a project with an Arduino Mega. The Arduino was being powered with a 9V battery plugged into the 5v and GND pins on the board. I needed to make some changes to the code, and so plugged the Arduino into my laptop's USB port with the 9V still connected. My laptop immediately shut off, making me think I either shorted or over-volted the port. I discovered that if I powered the arduino by connecting the battery to the Vin pin rather than the 5v, I could plug the Arduino into my laptop without issue and proceeded to work like this.

However, I noticed today that my laptop battery drains abnormally quickly when suspended (going from 100% to 50% in about two hours while asleep). Could the short from yesterday have damaged something internal?

Edit: Would just like to add that all USB ports on my computer appear to be functioning normally.

Yes... it sounds quite likely that one of the regulators has been damaged, and your laptop may succumb to high battery drain or even overheating / staying warm. Such regulators aren't often monitored... so I would turn it off, let it cool down, and then check for warm areas of the case (or possibly even take it apart)

To be honest I'm also surprised your Arduino is still working after a 9v injection - the ATMega2560 datasheet gives a "Maximum Operating Voltage" of 6v...

For future reference, it's really not a good idea to have two power supplies connected together. For example:

• Laptop 5v USB
• Arduino 5v regulator

Ideally, only power it from one source - laptop or battery.

If you need to power the Arduino from battery continuously, then look into disconnecting the 5v line between the computer and Arduino... this may require removal of a component, or a bit of work on an old USB cable.