http://www.optimabatteries.com/publish/optima/americas0/en/config/product_info/automotive.html<http://www.optimabatteries.com/publish/optima/americas0/en/config/product_info/automotive.html>

Combined Optima Batteries...

Vince....

Thanks for the response.  The little S/S screws actually don't so much act as the contact as they do a wedge, forcing a fine contact around most of the ring between the core and the outer ring.  Your solder suggestion is great.  If I had any welding talent, I might be able to fill what small gap remains, then remove the screws, and then fill that small hole as well.  

Like you, I wouldn't "preach" the combining of batteries.  I have used the same process on sailboats that race offshore (races from SoCal to Hawaii and Mexico) for years.  We are typically away from outside help for 6 - 12 days at a time.  Extra weight is a BIG thing on these boats (lighter is faster), and a dedicated starting battery that does nothing the other 23:59:55 of the day would be avoided.  

Since I never "isolate" my other battery, I could not see the purpose of a relay or other device.  In the attached photo from the Optima web-site, it looks like they are doing essentially what I have done.  Although, curiously, they appear to have joined their batteries in series, producing 32 volts if we are seeing all of the batteries involved.  What, do you suppose, runs better on 32 volts ????

I guess I'd take this as an Optima recommendation ??? for joining batteries.

Fin.