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How much battery charge to start engine

1848 Views 18 Replies 12 Participants Last post by jrcanoe, Apr 11, 2015

bshock

Discussion Starter · Apr 8, 2015

Hi All,

I'm scheduled to launch on April 17, and when I made the drive to the boat this past weekend to test the batteries, the starting battery (Group 31 lead acid) showed 12.52 on the multimeter, which according to a chart I found online is 85% charged. The battery is only a year old, and was topped off before winter storage (indoor heated), and ALL the batteries were disconnected from everything. This is the only battery that has dropped significantly, albeit slowly, during the winter. The two 4D's are still showing more than 12.7 on the multimeter.

Is the Group 31 at 12.52 enough to start the engine (Westerbeke 30b3 diesel) in a couple weeks?

As always, thanks so much for any help!

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Maine Sail

· #6 · Apr 8, 2015

If that battery can't start a 30B3, even if it were at 11.9V, it is toast.....

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Maine Sail

· #11 · Apr 10, 2015 (Edited)

Delta-T said:
You don't want to top off your batteries in the winter with water unless you are going to do a charge that will create a bubbling of the batt. acid. to mix it. Otherwise the water can freeze on the top.

Excellent point !!! This point can not be emphasized enough!!

Once topped up with water batteries need a good "rolling" charge, usually well in excess of 14.6V in order to properly mix the electrolyte and prevent stratification of the electrolyte.

Delta-T said:
If the batts are fully charged in the fall and are disconnected, there will be no discharge. As Main Sail has drilled thru or heads now for many years.

I like to see all flooded batteries charged to "full" (14.6V - 14.8V to at least 1% of capacity in accepted charge current) then equalized before winter.

The odd battery out on this one could just be a bad/weak cell or the fact that it was not sufficiently charged in the fall, for a long enough duration or at too low a low voltage.

Also this was indoor heated storage where the battery self discharge will be higher that sitting outside and stored colder. Either way it should easily start the motor...

bshock said:
Hi All,

The battery is only a year old, and was topped off before winter storage (indoor heated), and ALL the batteries were disconnected from everything.

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