Attiny85 to RST on ESP 12E help

I have an attiny85 connected via Pin 0 to reset pin on ESP 12E and it works to reset the ESP when both boards are connected to USB by sending LOW HIGH signal. However, when I run the attiny off of a 3V or 3.6V battery and the ESP off of usb, it no longer works to reset the ESP. I know ESP has wake from deep sleep ability but I was trying to have the attiny wake the board for my project. Is this a voltage issue, since 5V comes out of USB? If so, suggestion on how to fix this? Thank you in advance.

Are your grounds tied together? A very common mistake. A schematic would be useful.

Attaching them to the same ground solved it!! Thank you!

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