SailNet Community - View Single Post - 13 plus volts on rested battery?
View Single Post
post #8 of Old 12-29-2012
Maine Sail
Senior Member
Maine Sail's Avatar
Join Date: Jan 2003
Location: Maine Coast
Posts: 6,412
Thanks: 22
Thanked 305 Times in 236 Posts
Rep Power: 18
Re: 13 plus volts on rested battery?

Originally Posted by Rockter View Post
Barquito :

It is notoroiusly difficult to judge a battery condition by measuring the battery voltage, unless the battery is completely dead at (like) 12V or something similar.

Over the years, I have found that the only test is to charge it up, and work it to see if it meets a reasonable load, then re-charge it and see if it holds charge.

When your motor is charging, the battery voltage should be at about 14.1 V (or near to).
This is correct. A "rested" open circuit voltage is very accurate to determining SOC however. What it is NOT capable of is telling you what "capacity" you have left in the battery.

You can have a 100Ah battery reading 12.72V rested that will supply 100Ah. You can also have a 100% full 100Ah battery reading 12.72V that only has 60Ah of capacity left in it. Both batteries are at 100% state of charge but one now has less capacity due to use.

The only true measure of capacity is to do a controlled 20 hour capacity test at 80F... The Midtronics analyzers are also fairly accurate for looking at aging, if a when new baseline was taken, but they cost $600.00 to $2000.00... They still don't do a 20 hour "capacity" test or directly correlate over to capacity....

-Maine Sail / CS-36T

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Images In Posts Property of Compass Marine Inc.

Last edited by Maine Sail; 09-14-2014 at 05:36 PM.
Maine Sail is offline  
Quote Share with Facebook
For the best viewing experience please update your browser to Google Chrome