What it is?

[alanint]

This image of the complete M3 setup will give you an idea of the size of the battery pack for the Infrared night vision. This was the state of the technology in the Korean War era.

[sheepherder]

Originally Posted by alanint

This image of the complete M3 setup will give you an idea of the size of the battery pack for the Infrared night vision. This was the state of the technology in the Korean War era.

It's interesting that you chose that picture, as it looks like a direct contemporary copy of the Vampir...The attached pic is the one that seems to be the most popular for those writing about the M1/M3 w/IR scope...But more advanced...

The battery is clearly labeled 'battery'...

And looking at the three fluid inspection ports at the top, it looks like a lead/acid battery...