[C320-list] 10V battery-how?, alt to Exide, charging different batteries?

[Pat Ireland]

10V battery-how?, alt to Exide, charging different batteries?

One battery registered a bit over 10V when checked on Sunday.  Charged for
about 10 minutes and checked again.  Both batteries registered close to
13V.

Upon inspection, one of the battery terminals showed some corrosion, so I
cleaned all of the connections.  While the ground was off each battery, the
voltage registered about 10V.  When all assembled, both batteries registered
about 12.75V.  Both batteries started the engine with no problem.

It looks like we initially had one battery isolated from the buss with
corrosion.  The charger broke through that corrosion to establish
continuity.

Is that analysis likely correct, or is it more likely that the battery has
an internal short on one cell that was removed by the charger?

Given option 2, it's time to replace the batteries.  Really like the Exide
commercial option, but no dealers in the area.  CA is sunny but not all is
rosy.   Is the Exide sold under any other brand?  Interstate has an 4D-XHD
that sounds quite similar.  1000CCA, 1250CA......  Any possibility that it
is the same battery?

Also, the normal advice is to replace both batteries when one goes bad.
Logical, except, that with the addition of a starting battery in position 1
and connecting both 4Ds as a house battery in position 2, you get two
significantly different batteries.  How does the charging balance?  I can
understand the mode of operation where you keep the two banks isolated, but
It was my understanding that both banks get charged regardless of switch
position.

DC Challenged, Pat, 801