Looking at the parts diagram.....it does look like it would be a connection for a tender?? I have never snowchecked or owned one with electric start, so I'm not 100% sure.
Again, looking at the parts diagram, it appears as if that would be number 20, which is part of the electric start wiring harness.
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Yes, battery tender or similar will plug right in.
One can also buy an adapter for nicer CTEK chargers or the like.
One note, there is a fuse between that connector and the battery. Put a multimeter to the terminals to verify it is connected before you trust it to charge or maintain the battery. I learned the hard way...