While out on the water last weekend I have noticed the battery meter was reading as low as 10.5v after having the anchor light on overnight, etc. Since there is a generator aboard I wasn't particularly concerned. However, for a good measure, I purchased new 8D batteries and drove down to the marina. I have 2 8D batteries in the aft of engine room and 2 8D batteries in the engine room bilge. There is one additional 8D battery dedicated for the generator in the lazarette. With the exception of the latter all 4 batteries in the engine room are original batteries from 2006 (or as early as 2005) so they are due for change out.
I was expecting one set of those 2 8Ds to be house batteries and the other set to be dedicated engine w/ higher CCA. However when I opened up the battery boxes and panels I was surprised to find all those batteries interconnected. They are configured as shown on the attachment as "method 4".
Now the kicker is one set of batteries were reading 11.9v and the other set showing 13.7v. These measurements were taken while the battery charger was on w/ shore power so I understand these are not true reflection of their voltage.
My questions are:
1. Shouldn't all 4 batteries show the same voltage when they are interconnected? If so what would explain this discrepancy?
2. Should I leave them as they are configured or should I try to re-wire them so that I have 2 dedicated house and 2 dedicated engine batteries?
3. If I were to leave them as they are should I change them out w/ higher CCA batteries or house batteries?
Thanks much for your input.