13 plus volts on rested battery? - Page 2 - SailNet Community

   Search Sailnet:

 forums  store  

Quick Menu
Boat Reviews  
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Hatches and Portlights
Interior And Galley
Marine Electronics
Other Items
Plumbing and Pumps
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here

Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
 Not a Member? 
Old 12-29-2012
Maine Sail's Avatar
Senior Member
Join Date: Jan 2003
Location: Maine Coast
Posts: 5,745
Thanks: 17
Thanked 186 Times in 145 Posts
Rep Power: 16
Maine Sail is just really nice Maine Sail is just really nice Maine Sail is just really nice Maine Sail is just really nice
Re: 13 plus volts on rested battery?

Originally Posted by btrayfors View Post

As noted above and elsewhere, the only reliable tests of remaining capacity are either a 20-hour test or the use of a modern (and expensive) tester like the Midtronics series.

Gels are tricky. I've got two golf-cart size gels in my basement shop right now which are pushing 15 years old, the first 10 in use on a sailboat. Been using them for testing and for utility the past five years. One of these still measures more than 90% of original capacity; the other measures a bit lower. I use a Midtronics MDX-650....much easier than the 20-hour tests, but I do those, too.


I still find that even with Midtronics equipment you really need to start with a baseline. Once you have a baseline on a "broken in" bank future tests are far more telling in tracking actual changes to the battery.

Problem with a 20 hour test is that it has to be performed as a 20 hour test and at 77-80F. I built my own tester using a Victron monitor, Omron cube relay and constant current DC load.

*Bring battery to 77F
*Charge battery to full
*Allow battery to rest for 24 hours
*Program & reset Battery monitor
*Apply 20 hour load for battery (100Ah battery = 5A, 125Ah battery = 6.25A)
*Set Victron internal relay to cut test at 10.5V
*Read Ah's removed from battery

Anything less than a true 20 hour capacity test is only an approximation. I do prefer a Midtronics with "baseline" as it is much easier to track performance but it NEVER lines up with Ah capcity. Problem with any analyzer without a baseline is that many batteries produce better CCA or MCA than what they are rated for when new and broken in.

Testing batteries for capacity when cold is going to be inaccurate as Ah capacity goes down when cold. The 20 hour load will actually be higher to the battery capacity than it would be at 77F. In other words that 5A load at 30F is more like a 10A load at 77F.

Always best to mimic the industry test which is Ah capacity divided by 20 = load, until the bank reaches 10.5V. So (100Ah / 20 = 5A load). It should go 20 hours before hitting 10.5V if the battery is hitting its rated capacity. Counting the Ah's consumed before 10.5V is attained will tell you the Ah capacity as the battery sits currently.

I like my Midtronics & Argus but it is not an accurate representation of Ah capacity..
bhcva likes this.
-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; 02-27-2015 at 09:04 AM.
Reply With Quote Quick reply to this message Share with Facebook
Old 04-02-2013
Junior Member
Join Date: Nov 2012
Posts: 4
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
jorn85 is on a distinguished road
Re: 13 plus volts on rested battery?

The best way to test the battery is first it needs to be charged up, and then check if it meets the reasonable load. Again recharge the battery and verify if it holds the charge.
Reply With Quote Quick reply to this message Share with Facebook

Quick Reply

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Similar Threads
Thread Thread Starter Forum Replies Last Post
alternator volts vs. amps chuckg5 Electrical Systems 10 10-21-2011 01:39 AM
17 volts on a 12 volt system? FlyinNOE Electrical Systems 9 05-08-2009 12:54 AM
12 and 24 volts systems imsaint007 Electrical Systems 8 11-29-2008 06:40 PM
Troubleshooting Norcold works AC volts not DC volts chuck711 Gear & Maintenance 3 10-20-2006 02:39 PM
110 Volts on Board Tom Wood Gear and Maintenance Articles 0 07-07-2003 08:00 PM

All times are GMT -4. The time now is 04:33 AM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2015, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.