Somehow or another my post to this with an update didn't make it.
Anyhow...

The problem was my Morningstar Tristar voltage regulator. According
to the manual if you push the (only) switch for 5 seconds, the unit it
supposed to drop into manual equlaization mode until you push the
switch for 5 seconds again. I did this, but it seems that it didn't
go into manual equalization mode. It was diverting any voltage above
14.2 V to the water heater. I found out the hard way that I can boil
water in my water heater!

I haven't had a chance to re-run the equalization. I'll do that in
the next day or two. I'm busy installing a new water maker.

-- Geoff

P.S. Larry, thanks for the info regarding hydrogen production in new
batteries. I didn't know that.