I have an AtomS3 connected to an 8Encoder.
On direct USB power, the Atom recognizes the 8Encoder on I2C address 0x41 as expected in the spec and everything works fine.

I want to make the prototype portable, so I got a TailBat to provide power on the go.
The documentation says the Port.A pins are connected straight through, so everything should work the same.
HOWEVER, when I connect the 8Encoder through the TailBat, the 8Encoder is no longer found on 0x41.
Instead, when doing an I2C scan, I get a peripheral come up on 0x54, and my encoder is no longer recognized. (The encoder doesn't work on 0x54.)

FURTHER, on disconnecting the TailBat, the encoder CONTINUES to "register as 0x54" (or whatever is going on) for a while even when connected directly to the AtomS3.
I have no idea why or how this could be possible!

My only guess is that something is happening in the signal path to mess with the encoder, and it is retaining some charge that means it doesn't reset for several minutes.

If someone could shed some light on it, I would be grateful!

Evidence..

Connected directly - works!

Connected via TailBat - doesn't work

Connected directly again - STILL doesn't work!!