I ran across a coach battery that had a reversed polarity measuring about -2v. When connected to the other 6 volt battery, the net result was only about 4 v. I don't know how old the battery was because the month and date on the battery was not punched or marked, but I'm guessing a few years old.

Has anyone else experienced this?

The service technician from a golf cart store that handled Trojan batteries said he's seen this but didn't know what caused it.  The solution was simply to replace the battery.  All is back to normal, now.