Hi,
If it is turning itself off, it could indicate liquid is still present on the board, which could not be cleaned out using a brush. Try to take it to someone who will be able to ultrasonic clean the board, to ensure it is thoroughly cleaned.
Try booting without the battery disconnected, and also feel the logic board (mainly the chips) to see if anything is getting hot. If you can feel heat (coming from a chip other than the CPU or GPU obviously) the chip or a component on the same path to the chip is being shorted to ground. Replacing the chip at this point should resolve the issue, and if not, you will need to replace the component which is bringing the signal to ground.
Where was the liquid damage originally, are you able to send across a picture? Have you also removed the whole logic board, or tried a test keyboard to ensure this is not the issue?