That's a hidden anti-theft switch to disable the entire battery system,
one of several levels of disabling I built into it. The ground cable:
this photo was an 'unfinished' photo, as shortly after I routed the
ground cable over to the other side to combine with the ground of that
battery, both of which then routed to a shunt for the Victron battery
monitor. I'll see if I can locate a photo of the final connections.
Otherwise, without the shunt inline, the ground would go directly to
that stud near it.

On 6/10/2021 7:15 AM, Steve Williams wrote:
> Karl, in that photo, what's the keyed thingie?�  And where is the battery
> strap grounded when in use?
>
> On 6/9/2021 1:38 PM, Karl wrote:
>> ... http://westyventures.com/batterybox%20(6).JPG