The plastron (bottom shell) is hinged, allowing it to withdraw into its shell and ”box” itself in completely, leaving no body part exposed.
Turtles that I had encountered before cannot pull their legs in completely like Batu. As such, I deduced that Batu is not a turtle and therefore must be a tortoise.
One Big Mistake! Only turtles have webbed feet!
Batu's webbed feet above.
The webbed feet can be seen only when the photo is cropped and enlarged.
After a bit of research, Batu should be a Malayan Box Turtle. Only Malayan Box Turtle has 3 unique yellow stripes on each side of its head. It grows to 7.5" only. So Batu has reached its adult size. It has a docile temperament unlike snapping turtles which are very aggressive.
A male has a thick tail as well as a slight plastral concavity. A female has a short stubby tail as well as a completely flat plastron. Batu has a slightly concave plaston and look at his thick long tail below.
Clear information on differentiating male and female were found here.
There is definitely insufficient water feature in my garden for Batu at the moment since I had made the assumption that it's a tortoise. I am thankful that it has rained daily since Batu arrived. Fortunately, we had also been wetting him when the weather was hot to prevent dehydration.