Serial Batteries CCA and RC Question

[corsa59]

At present in my boat I have 2 banks of batteries, each bank is 4 batteries in series (6 volt, CCA 770, RC 260). The batteries are basically used to start the main engine once and only once before a charter, then the 24 volt system supplies power to virtually nothing during the charter other than the navigation lights and the instrument panel in the wheelhouse, I assume that most of this power is generated by the alternator anyway, so the batteries virtually are not required after starting.

Both banks are fast approaching the end of their useful life, and I have this question. Please explain why I need 4 6 volt batteries, wouldn't 2 12 volt batteries do the same job.

Obviously connecting 4 6 volt batteries is series creates 24 volts just like 2 12 volt batteries, but is the CCA or RC different? Does the CCA change when you link batteries in series? Does the RC do likewise? Is there a formula to calculate these increases?

Any help would be appreciated.

 

[sreid]

First;

Cold cranking amps (CCA) is the amount of current a battery can provide at 0°F (?18°C). The rating is defined as the amperage a lead-acid battery at that temperature can deliver for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12-volt battery).

Reserve capacity minutes (RCM), also referred to as reserve capacity (RC), is a battery's ability to sustain a minimum stated electrical load; it is defined as the time (in minutes) that a lead-acid battery at 80°F (27°C) will continuously deliver 25 amperes before its voltage drops below 10.5 volts.

My understanding is that multiple batteries are used in boats so they can fit the space available. You can use 2 12 V batteries (or 1 24V battery) but you will find that for the same CCA and RC, the 12 V batteries will not have the same dimensions.

 

[IRstuff]

CCA is intrinsic in the design of the plates, electrolyte, and spacings.

TTFN

FAQ731-376