locked Southern SD-45's


in the past months I have studying pictures of Southern SD-45 fleet.  I have found one item very curious and can find no information about it.
The item in question is an extension of the battery box on the short hood end conductors side as seen below.

This extension appears on most SD-45's from 3106 thru 3160 or so.  Can anyone explain what this was used for,  also it appears on the SD35's as well.
I am posing this question on several lists so please forgive in duplication.

Thanks in advance,
James Wall
Rural Hall, NC

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