Backhoe JD 300-C battery configuration

[JCWilk]

To anyone willing to assist,
My two 6 volt batteries (BCI NO.3EH; CCA1075/875-32degrees F/0degrees F) for my JD300-C backhoe/frontloader died and in replacing them I embarrassingly failed to note the proper configuration; are they in series or in parallel? I do not want to burn out my alternator with ignorant placement. The tractor is several decades old (precise year unknown) with no manual.
Humbly
JCWilk

 

[JCWilk]

OOPS!!, JD 500-C backhoe/front loader, not 300-C. Is the battery configuration for the two 6volt batteries in series or parallel?
thx
JCWilk

 

[JCWilk]

Wired in series for a 12 volt system.

Many Mahalos!!