Vintage Sony integrated circuit transistor radio, mini handheld radio

Vintage Sony integrated circuit radio, a cute little thing just 4 1/2" long. The original case is kind of worn.

We couldn't figure out how to open this up to check the battery - all we know it that it's not working, though it might be an easy fix? Maybe it's a re-chargeable radio, but if so, it's missing the cord.