Journey with Confidence RV GPS App RV Trip Planner RV LIFE Campground Reviews RV Maintenance Take a Speed Test Free 7 Day Trial ×


Reply
 
Thread Tools Display Modes
 
Old 10-28-2018, 07:57 PM   #1
Bus Crazy
 
Ronnie's Avatar
 
Join Date: Oct 2017
Location: Virginia
Posts: 2,324
Year: 1971
Coachwork: Wayne
Chassis: International Loadstar 1700
Engine: 345 international V-8
optima battery how to tell when fully charged

I have optima batteries, and would like to know how to tell when they are fully charged. I have heard that voltage is not an accurate way to tell, and because it is an AGM battery it is not possible to use a hydrometer. My understanding of a battery monitor is it counts what goes in and what goes out, well enough if the battery is starting at a full state of charge, of course that gets me back to what is a full state of charge? So what am I missing here?

Ronnie is offline   Reply With Quote
Old 10-28-2018, 08:21 PM   #2
Bus Crazy
 
joeblack5's Avatar
 
Join Date: Dec 2015
Location: pa
Posts: 2,498
Year: 98
Coachwork: 1. Corbeil & 2. Thomas
Chassis: 1 ford 1998 e350 4x4 7.3 2 mercedes 2004
Engine: 7.3 powerstroke & MBE906
good point.Very hard to tell. For lead acid they "invented" float charge. That is a voltage of 13.5 to 13.8 volt at 25 degree Celsius. At that voltage it keeps charging a small amount all the time. The excess electricity is wasted in heat and off gassing. For AGM and zero maintenance the gasses are recombined in the battery so that no electrolyte gets lost.
So after your charger has bulk charged , topping charge and float chargedyou can consider it full.


If you have a true battery monitor that counts ah in and ah out... it needs to have a shunt in series with all loads and all chargers...then you can check the real capacity of your battery by discharging to 11.6 volt with a relative low current . only once in a while because discharging 100% is bad for your lead acid battery.
joeblack5 is offline   Reply With Quote
Old 10-28-2018, 08:27 PM   #3
Bus Geek
 
Join Date: Nov 2016
Posts: 2,775
You measure declining amps while holding Absorb voltage.

When it gets to .005C they are Full 100% and you drop to Float.

That is half an amp per 100AH.

Old worn batts may not get there, so can use

amps drop less than .1A in an hour

instead.
john61ct is offline   Reply With Quote
Old 10-29-2018, 07:00 AM   #4
Bus Crazy
 
Ronnie's Avatar
 
Join Date: Oct 2017
Location: Virginia
Posts: 2,324
Year: 1971
Coachwork: Wayne
Chassis: International Loadstar 1700
Engine: 345 international V-8
Quote:
Originally Posted by john61ct View Post
You measure declining amps while holding Absorb voltage.

When it gets to .005C they are Full 100% and you drop to Float.

That is half an amp per 100AH.

Old worn batts may not get there, so can use

amps drop less than .1A in an hour

instead.
Ok this makes sense to me.

Does the battery offer more resistance to charging as it gets full? and that is why the charge rate drops?
Ronnie is offline   Reply With Quote
Old 11-08-2018, 10:01 AM   #5
New Member
 
Join Date: Oct 2018
Posts: 8
I came across the following link that may be helpful - very long and detailed

https://marinehowto.com/programming-a-battery-monitor/

Toward the end it talks about how to know your battery is at 100% so that you can reset your Ah meter.
Heleads is offline   Reply With Quote
Old 11-08-2018, 12:05 PM   #6
Bus Geek
 
Join Date: Nov 2016
Posts: 2,775
Quote:
Originally Posted by Ronnie View Post
Ok this makes sense to me.

Does the battery offer more resistance to charging as it gets full? and that is why the charge rate drops?
Exactly. And MaineSail's site above is well worth close study
john61ct is offline   Reply With Quote
Old 11-08-2018, 12:43 PM   #7
Bus Crazy
 
Ronnie's Avatar
 
Join Date: Oct 2017
Location: Virginia
Posts: 2,324
Year: 1971
Coachwork: Wayne
Chassis: International Loadstar 1700
Engine: 345 international V-8
Thanks, am looking at the link now. It certainly is detailed, and so far seems to be what I am looking for.
Ronnie is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Featured Campgrounds

Reviews provided by

Powered by vBadvanced CMPS v3.2.3

All times are GMT -5. The time now is 06:39 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2024, vBulletin Solutions, Inc.