Let's say the Mice are X and Y and Bottle are B1, B2....B9

Step1:

X drinks B1 B2 & B3

Y drinks B1 B4 & B5

Possible Outcomes

If both mice die, B1 is the poison bottle.

If only mice X dies, Either B2 or B3 is the poison bottle.

If only mice Y dies, Either B4 or B5 is the poison bottle.

If nobody dies, Poison is in B6 B7 B8 or B9

Step2: (If nobody dies)

X drinks B6 B7

Y drinks B6 B8

Possible Outcomes

If both mice die, B6 is the poison bottle.

If only mice X dies, B7 is the poison bottle.

If only mice Y dies, B8 is the poison bottle.

If nobody dies, B9 is the poison bottle.

Step2: (Only X dies - Either B2 or B3 is the poison bottle)

Y drinks B2, if Y dies B2 is the poison bottle else B3

Step2: (Only Y dies - Either B4 or B5 is the poison bottle)

X drinks B4, if X dies B4 is the poison bottle else B5