RV Trip Planning Discussions

Go Back   iRV2 Forums > RV SYSTEMS AND TECHNOLOGIES FORUMS > RV Systems & Appliances
Click Here to Login
Join iRV2 Today

Mission Statement: Supporting thoughtful exchange of knowledge, values and experience among RV enthusiasts.
Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on iRV2
 
Thread Tools Search this Thread Display Modes
 
Old 10-21-2018, 08:03 PM   #1
Member
 
Join Date: May 2015
Posts: 42
Please advise....AGM Battery Charge Information

Hi All,

Please help me understand what the real story is. I'm reading conflicting data on what a fully charged AGM battery is. After charged it reads 12.9, then ten seconds later, 12.8, then ten seconds later 12.7. This is with no load. When I add a very light load, it will drop down from 12.7 to 12.5 after 10 minutes or so and stay there for a long time. I read not to let the battery go below 12.5 so I'm reluctant to do so and I end up turning on the inverter again to keep it topped off. The reason I turned the inverter off is to "test" the battery while it's new/under warranty to see how it's acting. I expected it to stay at 12.9v until I begin to deplete it. The attached thumbnails show what Duracel says then also what another website says. Please educate me...thank you!
Jim


Specs on the Brand NEW Duracel AGM Battery:
20 amp hour rate: 92
Battery electrolyte composition: glass mat
Battery purpose: starting/deep cycle
BCI group size: 27M
Reserve capacity: 175
Terminal type: stud and post
Volts: 12

Battery Link:
https://www.samsclub.com/sams/marine...lp_product_1_7

Middle thumbnail Battery FAQ link:
Deep Cycle Battery FAQ
Attached Thumbnails
Click image for larger version

Name:	Battery1.jpg
Views:	123
Size:	47.4 KB
ID:	223370   Click image for larger version

Name:	Battery2.jpg
Views:	117
Size:	24.1 KB
ID:	223371  

Click image for larger version

Name:	Battery3.jpg
Views:	108
Size:	19.6 KB
ID:	223372  
__________________

__________________
2003 Coachmen Freedom 289qb - 2002 Chevy Express 3500 Chassis
jimvette999 is offline   Reply With Quote
Join the #1 RV Forum Today - It's Totally Free!

iRV2.com RV Community - Are you about to start a new improvement on your RV or need some help with some maintenance? Do you need advice on what products to buy? Or maybe you can give others some advice? No matter where you fit in you'll find that iRV2 is a great community to join. Best of all it's totally FREE!

You are currently viewing our boards as a guest so you have limited access to our community. Please take the time to register and you will gain a lot of great new features including; the ability to participate in discussions, network with other RV owners, see fewer ads, upload photographs, create an RV blog, send private messages and so much, much more!

Old 10-21-2018, 08:29 PM   #2
Senior Member
 
Join Date: Aug 2017
Posts: 892
It could be your battery is not being fully charged. Most AGM batteries should be charged at 14.2 to 14.4 volts for 8 to 12 hrs to fully charge them. Once fully charged , the voltage will sit at 12.9 volts for quite some time. Under load the voltage will drop , but should come up once the load is removed.
__________________

__________________
1993 Tiffin Allegro Bay 32'
Soppy is offline   Reply With Quote
Old 10-21-2018, 08:47 PM   #3
Member
 
Hoosier14's Avatar
 
Join Date: Feb 2018
Location: Indiana
Posts: 53
Immediately following charging, a 12v battery will have a surface charge above the resting voltage. The 12.9 number is a surface charge and your battery should not stay at this level. A fully charged 12v battery should be considered full at 12.7 volts. At 50%, the battery would be 12.2 volts. You donít have a lot of amps available so even a light load will pull the battery voltage down some. Also know that by adding a heavy load you could easily and quickly drop below 12.2v. This does not mean the battery needs charged. Take the load off and if the battery is still below 12.2 with the load off, it needs charged.
__________________
Hoosier14
Prevost, 45í, DD Series 60
Country Coach Conversion
Hoosier14 is offline   Reply With Quote
Old 10-21-2018, 09:10 PM   #4
Member
 
Join Date: May 2015
Posts: 42
Quote:
Originally Posted by Soppy View Post
It could be your battery is not being fully charged. Most AGM batteries should be charged at 14.2 to 14.4 volts for 8 to 12 hrs to fully charge them. Once fully charged , the voltage will sit at 12.9 volts for quite some time. Under load the voltage will drop , but should come up once the load is removed.
Thank you... I will investigate putting it on my charger and seeing if it's not actually fully charged.


Quote:
Originally Posted by Hoosier14 View Post
Immediately following charging, a 12v battery will have a surface charge above the resting voltage. The 12.9 number is a surface charge and your battery should not stay at this level. A fully charged 12v battery should be considered full at 12.7 volts. At 50%, the battery would be 12.2 volts. You don’t have a lot of amps available so even a light load will pull the battery voltage down some. Also know that by adding a heavy load you could easily and quickly drop below 12.2v. This does not mean the battery needs charged. Take the load off and if the battery is still below 12.2 with the load off, it needs charged.
Thank you, but as you can see, I'm already getting conflicting information. My top Thumbnail from Duracel, the battery brand and Member Soppy, both indicate that the AGM should have a resting charge level of 12.9 volts when at 100% charge level. You say it should be at 12.7 volts. Additionally, respectfully, you didn't address my question/concern about the weird voltage drop.
__________________
2003 Coachmen Freedom 289qb - 2002 Chevy Express 3500 Chassis
jimvette999 is offline   Reply With Quote
Old 10-21-2018, 09:25 PM   #5
Member
 
Hoosier14's Avatar
 
Join Date: Feb 2018
Location: Indiana
Posts: 53
With agm, they can actually have a slightly higher resting voltage, up to 12.9. After rereading your post, if your batteries specs say that they should be fully charged at 12.9, the only issue I could see other than the resting voltage being lower than 12.9 as I assumed, would be a draw on your battery. For instance, I have two inverters, but I also have 12v draws that donít go through either inverter. Therefore, I still have amp draws with the inverters off. The only way to know how the battery voltage is right after a charge and hours later at rest would be to fully charge the battery, disconnect it, then take voltages directly at the battery with a voltage meter.
__________________
Hoosier14
Prevost, 45í, DD Series 60
Country Coach Conversion
Hoosier14 is offline   Reply With Quote
Old 10-22-2018, 07:16 AM   #6
Member
 
Join Date: May 2015
Posts: 42
Quote:
Originally Posted by Hoosier14 View Post
With agm, they can actually have a slightly higher resting voltage, up to 12.9. After rereading your post, if your batteries specs say that they should be fully charged at 12.9, the only issue I could see other than the resting voltage being lower than 12.9 as I assumed, would be a draw on your battery. For instance, I have two inverters, but I also have 12v draws that don’t go through either inverter. Therefore, I still have amp draws with the inverters off. The only way to know how the battery voltage is right after a charge and hours later at rest would be to fully charge the battery, disconnect it, then take voltages directly at the battery with a voltage meter.
Thank you. I do have a battery disconnect I use and the battery resting voltage seems to be at 12.7. I have a small built it digital display I use and everytime I check it it's at 12.7. I run a trickle charger on a timer that hits it for an hour twice a day to keep it topped. The post I made was what I was experiencing on my first trip out while actually using the battery on a trip. I just noticed that the charge dropped from 12.9 rather quickly in my opinion from 12.9 to 12.7 to 12.6 to 12.5 then hung there. I was under the impression that it should start out at 12.9 and "gradually" drop based on the very light load I had on it. I really do appreciate the replies, I plan to let the inverter stay on it for 8-10 hours today and see if Soppy's theory is right....may be I never really "filled it up".
Jim
__________________
2003 Coachmen Freedom 289qb - 2002 Chevy Express 3500 Chassis
jimvette999 is offline   Reply With Quote
Old 10-22-2018, 09:04 AM   #7
Member
 
Triple E Owners Club
Join Date: Jul 2017
Posts: 50
As other forum members have noted, if the AGM battery is new then 12.7V is low if there are no loads present, the battery is fully charged and the temperature is around 75F. If the battery is older then 12.7V would not be unexpected.

The best way to know when the battery is fully charged is by observing the amp flow into the battery. At 14.4V I'd charge until the rate of charge acceptance drops to around 0.5A.

If you're not able to measure amps in then you're left with charging for long enough to get the battery fully charged.

The final 10% of charging will take much longer than you'd expect. One of the Deka battery brochures shows an example of it taking 3 1/2 hours to get to 90% and a further 2 1/2 hours for the last 10%. If off grid and you are charging by generator then getting to 90% is a good enough goal. Solar charging is a good option to get the final 10% in.

Temperature also has an effect. Most battery state of charge charts are calculated for temperatures between 70F and 80F. If it is colder than that where the battery is then expect to see a slightly lower open circuit voltage.
__________________
2002 Triple E on 2002 F53 Chassis
RV2traveler is offline   Reply With Quote
Old 10-22-2018, 09:20 AM   #8
Senior Member
 
757driver's Avatar


 
Entegra Owners Club
Join Date: Jun 2004
Location: Cambridge, Ontario
Posts: 3,162
Jim,

You will know your batteries are fully charged when the voltage is at 14.4-14.6v and the charge current has reduced to a low level (around 5amps or less).

If you are using your coach the SOC tables are not much use because your batteries are not at rest. An average in use 50% SOC voltage for AGM batteries is about 11.9-12.0v. The warning that said to recharge your batteries at 12.5v is not practical or very efficient.

ALL lead acid batteries can be discharged up to roughly 80%, BUT if you regularly discharge them that far then you shorten their life span but you do not kill them. That is why most try to keep the DOD (depth of discharge) to 50% and then recharge. This gives a good average of in use time between recharges and life cycles.

The best thing you can do for your batteries is keep them fully charged. The worst thing you can do is discharge them and leave them sit for an extended period of time without recharging.

With regards to charging if you are without shore power use them as you see fit down to about 50% and then recharge with a generator up to about 80% and stop. This will take about 2-2.5 hours. To get the last 20% would take another 3-4 hours of generator run time which is inefficient. Once back on shore power (or once a week) fully recharge your batteries.

By the way a flooded battery at rest should read about 12.7v at 100%. An AGM battery at rest should read about 12.9v at 100%.
__________________
Don & Gerri
2014 Entegra Anthem 44B
2014 Honda CRV Touring

1100W Solar, 1200AH LiFePO4 FMCA F443497
757driver is offline   Reply With Quote
Old 10-22-2018, 09:34 AM   #9
Senior Member
 
Mr_D's Avatar
 
Country Coach Owners Club
Winnebago Owners Club
Solo Rvers Club
iRV2 No Limits Club
Join Date: May 2011
Location: Vancouver, WA
Posts: 33,506
A lot of people in the know say to set the auto gen start at 12.3 volts.
__________________
2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft
Charter Good Sam Lifetime Member, FMCA, SKP
RV'ing since 1957, NRA Benefactor Life, towing '14 CR-V
Mr_D is offline   Reply With Quote
Old 10-22-2018, 12:03 PM   #10
Member
 
Join Date: May 2015
Posts: 42
Quote:
Originally Posted by RV2traveler View Post
As other forum members have noted, if the AGM battery is new then 12.7V is low if there are no loads present, the battery is fully charged and the temperature is around 75F. If the battery is older then 12.7V would not be unexpected.

The best way to know when the battery is fully charged is by observing the amp flow into the battery. At 14.4V I'd charge until the rate of charge acceptance drops to around 0.5A.

If you're not able to measure amps in then you're left with charging for long enough to get the battery fully charged.

The final 10% of charging will take much longer than you'd expect. One of the Deka battery brochures shows an example of it taking 3 1/2 hours to get to 90% and a further 2 1/2 hours for the last 10%. If off grid and you are charging by generator then getting to 90% is a good enough goal. Solar charging is a good option to get the final 10% in.

Temperature also has an effect. Most battery state of charge charts are calculated for temperatures between 70F and 80F. If it is colder than that where the battery is then expect to see a slightly lower open circuit voltage.

Very, very helpful...thank you. I have a Fluke amp meter that I can check amp inflow with. I'm charging it now with the inverter...the volt meter I have attached to the poles of the battery read 13.5 volts steady state so I'm not sure if it's ready the inverter output volts or the battery volts...the amp measurement should tell me something.
Jim
__________________
2003 Coachmen Freedom 289qb - 2002 Chevy Express 3500 Chassis
jimvette999 is offline   Reply With Quote
Old 10-22-2018, 12:07 PM   #11
Member
 
Join Date: May 2015
Posts: 42
Quote:
Originally Posted by 757driver View Post
Jim,

You will know your batteries are fully charged when the voltage is at 14.4-14.6v and the charge current has reduced to a low level (around 5amps or less).

If you are using your coach the SOC tables are not much use because your batteries are not at rest. An average in use 50% SOC voltage for AGM batteries is about 11.9-12.0v. The warning that said to recharge your batteries at 12.5v is not practical or very efficient.

ALL lead acid batteries can be discharged up to roughly 80%, BUT if you regularly discharge them that far then you shorten their life span but you do not kill them. That is why most try to keep the DOD (depth of discharge) to 50% and then recharge. This gives a good average of in use time between recharges and life cycles.

The best thing you can do for your batteries is keep them fully charged. The worst thing you can do is discharge them and leave them sit for an extended period of time without recharging.

With regards to charging if you are without shore power use them as you see fit down to about 50% and then recharge with a generator up to about 80% and stop. This will take about 2-2.5 hours. To get the last 20% would take another 3-4 hours of generator run time which is inefficient. Once back on shore power (or once a week) fully recharge your batteries.

By the way a flooded battery at rest should read about 12.7v at 100%. An AGM battery at rest should read about 12.9v at 100%.
Thank you, great info and battery strategy tips. I'm working on getting the thing fully charged now with shore powered coach inverter since that's what I have to work with while on trips. I have a generator too but don't do any boondocking so I just run it monthly for an hour at half load to keep it on the ready. Again...thank you
Jim
__________________
2003 Coachmen Freedom 289qb - 2002 Chevy Express 3500 Chassis
jimvette999 is offline   Reply With Quote
Old 10-22-2018, 12:09 PM   #12
Member
 
Join Date: May 2015
Posts: 42
Quote:
Originally Posted by Mr_D View Post
A lot of people in the know say to set the auto gen start at 12.3 volts.

Interesting....my coach is not fancy enough for auto start anything though...
Jim
__________________
2003 Coachmen Freedom 289qb - 2002 Chevy Express 3500 Chassis
jimvette999 is offline   Reply With Quote
Old 10-22-2018, 12:54 PM   #13
Member
 
Triple E Owners Club
Join Date: Jul 2017
Posts: 50
Quote:
Originally Posted by jimvette999 View Post
Very, very helpful...thank you. I have a Fluke amp meter that I can check amp inflow with. I'm charging it now with the inverter...the volt meter I have attached to the poles of the battery read 13.5 volts steady state so I'm not sure if it's ready the inverter output volts or the battery volts...the amp measurement should tell me something.
Jim
Knowing the amps in at 13.5V won't be that useful. 13.5V is more or less a float voltage used to maintain a battery. It's a bit on the high side for a float voltage but probably OK with an AGM battery. To get the battery fully charged you need to get the voltage up to 14.4 volts.

I use a Trimetric Battery Monitor in one application and set the parameters for the "Charged" indicator requirement to reaching 14.3V and accepting 1 amp or less current. That's on an older 400Ah AGM battery bank and it is easy to achieve that set point. A single newer 92Ah AGM battery should be able to get 14.4V and 1 amp or less current flow easily with a good charger.
__________________
2002 Triple E on 2002 F53 Chassis
RV2traveler is offline   Reply With Quote
Old 10-22-2018, 03:39 PM   #14
Member
 
Join Date: May 2015
Posts: 42
Quote:
Originally Posted by RV2traveler View Post
Knowing the amps in at 13.5V won't be that useful. 13.5V is more or less a float voltage used to maintain a battery. It's a bit on the high side for a float voltage but probably OK with an AGM battery. To get the battery fully charged you need to get the voltage up to 14.4 volts.

I use a Trimetric Battery Monitor in one application and set the parameters for the "Charged" indicator requirement to reaching 14.3V and accepting 1 amp or less current. That's on an older 400Ah AGM battery bank and it is easy to achieve that set point. A single newer 92Ah AGM battery should be able to get 14.4V and 1 amp or less current flow easily with a good charger.
I see. I have a 10 amp battery charger I can hook up to it....it's an older craftman charger though. It's automatic and the amps drop as the battery reaches charge, I was afraid to use it not know how many volts it was hitting it with knowing high volts (15+) is bad for sealed battery. I will hook it up and watch the volts.. I will look into a better charging device..... in the meantime here's some pics of what was going on. The battery does indeed read higher now when disconnected so I think with the help I've received from you guys, I'm on the right track to "filling it up". So appreciative to all that replied.
Jim
Attached Thumbnails
Click image for larger version

Name:	20181022_161315.jpg
Views:	58
Size:	218.3 KB
ID:	223435   Click image for larger version

Name:	20181022_161658.jpg
Views:	62
Size:	248.4 KB
ID:	223436  

__________________

__________________
2003 Coachmen Freedom 289qb - 2002 Chevy Express 3500 Chassis
jimvette999 is offline   Reply With Quote
Reply

Tags
battery



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

Advanced Search
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


Similar Threads
Thread Thread Starter Forum Replies Last Post
AGM Batteries/AGM Batteries Floridakamper Winnebago Industries Owner's Forum 8 09-19-2016 07:26 AM
When are AGM's not AGM's? bokobird iRV2.com General Discussion 39 09-24-2014 09:59 AM
General VRLA/AGM battery information TQ60 iRV2.com General Discussion 0 09-14-2012 01:33 PM
AGM that is rated for charge voltage of 15 volts? scottma Winnebago Industries Owner's Forum 5 04-15-2010 07:04 PM
AGM Batteries, Are You Happy With Your AGM's? Are They The Answer? Lug_Nut Newmar Owner's Forum 36 11-25-2007 08:59 AM

» Featured Campgrounds

Reviews provided by


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 04:53 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.