In accordance with another source, I have bought online and used a Phillips #0000 screw driver, which worked pretty well here. It costed me only $2 .

After replacing the battery, the old glue would lump up too thick, and also become too weak to fix the panel back to the outer case. I have scraped all the old glue off using a small flat head screw driver, and affixed a double sided adhesive tape cut into small strips, which was successful in both aspects.