How do you open the back off in order to change batteries on a threshold marquee light?

On the back of the metal light is a small plastic box for batteries. However, I cannot seem to get it off. There are no screws to remove. There is

On the back of the metal light is a small plastic box for batteries. However, I cannot seem to get it off. There are no screws to remove.
There is a slot that appears to be for a coin to remove the top, but it is hard to reach and it doesn't seem to work either!!

or:On the back of the metal light is a small plastic box for batteries. However, I cannot seem to get it off. There are no screws to remove. There is a slot that appears to be for a coin to remove the top, but it is hard to reach and it doesn't seem to work either!!

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