[C320-list] Electrical Problem

[Robert Seastream]

Did the mechanic 'load test' your batteries or simply check them with  
a voltmeter?  Voltmeters can't show current delivering capacity.  Four  
year old batteries should be OK, unless they were in a chronic  
'undercharged' state.  This can happen if (like me) you're on a  
mooring during the season without access to shore power and must rely  
on the stock alternator to charge the batteries during (usually short)  
motoring periods.  The stock alternator is rated for 55 amps and  
delivers about half that once derating for engine heat is considered.   
I replaced mine with one rated for 125 amps.  It charges my batteries  
from 25-50% to full charge in ~2 hours; much faster than the 4+ it  
used to take.  I also have a Honda EU2000i generator should the need  
arise.  We bought our 2002 in November 2005; I replaced the batteries  
in April 2008 to give us a known baseline.

Bob Seastream
Intuition # 906

On Oct 22, 2011, at 9:51 AM, Joseph Aberdale wrote:

> I have a very perplexing, troubling electrical problem that I would  
> very much appreciate your help with.
>
> My 2002  320 has two 4D banks of Interstate batteries that are 4  
> years old. For the past month I have been experiencing the  
> following.  If I don't start my engine once every 3 days, there is  
> not enough power in the batteries to turn it over to start. I then  
> have to use shore power to start it. Recently, I motored the boat  
> for 2 hours to get to the marina that hauls it out for the winter.  
> Upon arriving, the mechanic checked the batteries and determined  
> that they were fully charged and did not have any dead cells. I  
> turned the battery switch to "off" and had all of the circuit  
> breakers on the panel off as well. The bilge pump is not hard wired  
> to the batteries. I returned 3 days later and found the batteries  
> had some juice but if the engine did not start immediately, there  
> was not enough juice to try to start the engine a second or third  
> time. I then connected the shore power cord and it would not start  
> the engine. Several hours later with the shore power cord still  
> connected, there was enough juice to turn the engine over just twice.
>
> Could something be drawing down the batteries even though all of the  
> breakers are off?  Are the batteries bad after 4 years because they  
> cannot maintain a full charge for 3 days? Your thoughts and help are  
> appreciated. Thank you.
>
> Joe Aberdale
> #908