AGM charge level

[Gormley Green]

Battery knowledge is not my strength. With that in mind...

My new AGM after a smart charge settles at a max of 12.93v. After a few days it seems to be around 12.89 to 12.87v. My question: is there a normal "full" charge voltage, and what is the lowest I'd want the battery to go. I.e. what is the voltage range of one of these batteries, so I can determine a % charge (voltage)?

I'm sure this is on here somewhere but I can't find my specific answers.

Thanks.

 

[pods8]

What battery do you have? They all have slight differences. Also keep in mind, after a charger is removed they'll still show a bit higher voltage artificially until a bit of time has passed or a load has been applied to dissipate it. Mine sit around 13-13.1 when FULLY topped off and allowed to rest for a day.

Your numbers sound fine, for general purposes 12.8+V is usually considered charged, keep in mind a battery will self discharge as time passes as well.

 

[Gormley Green]

Thanks. It's a Deka Intimidator 79AH.

And I have noticed the decline after taking the charger off. It will take several hours to drop from over 13v to where it settles at 12.93. But typically the next day I'll be at around 12.89 or so.

 

[leadsled9]

Here is a basic guideline:

 

[pods8]

Specs on that battery are:
100% 12.8+
75% 12.6
50% 12.3
25% 12
0% 11.8

Also typical life cycles on Deka:
100% drawn = 150
80% drawn = 200
50% drawn = 370
25% drawn = 925
10% drawn = 3100

 

[Gormley Green]

Awesome. Thanks for all the info. This site is the best.

 

[LuckyDan]

Specs on that battery are:
100% 12.8+
75% 12.6
50% 12.3
25% 12
0% 11.8

Also typical life cycles on Deka:
100% drawn = 150
80% drawn = 200
50% drawn = 370
25% drawn = 925
10% drawn = 3100


Wow It's nice to know that I have a pretty good battery, (I think.) Mine's a DEKA 1131MF

 

[pods8]

Those kinda numbers are typical for AGMs and illustrate why folks are always saying to limit your depth of battery depletion on a regular basis. Better to have a bit more battery that only gets partially cycled and also has extra capacity for those times it's really needed than to constantly run down a smaller sized battery bank.

 

[portermoab]

Specs on that battery are:
100% 12.8+
75% 12.6
50% 12.3
25% 12
0% 11.8

Also typical life cycles on Deka:
100% drawn = 150
80% drawn = 200
50% drawn = 370
25% drawn = 925
10% drawn = 3100

Hey Pods- where did you pull those numbers? I was concerned about the same battery (Intimidator 8A24M, 79AH) so I called Deka. They said that my battery showing 12.57 was a full charge. Thoughts on that?

 

[Randonneur]

Understanding the best way to maintain my Exide Edge FP-AGM24DP battery that came with my 2017 Fleet has also been one of my weak spots. I have a Noco Genius 2 battery charger/tender and keep it plugged in when the camper is not in use. I connect it through the solar charging SAE port on the rear of the camper and in order to connect this correctly, you have to use a polarity reverser/adapter since the solar port is the opposite polarity for charging with a device. Keeping the battery charged when not in use mostly works this way and when I had the 4 year old batter checked at Batteries Plus last month they said it was still in good shape. Whenever I am using the camper the battery is kept charged either through driving or through a portable 140 watt Zamp solar panel that also has a monitor that I use to check on how good the battery is. A full charge using this will read 14.4 V which seems strange to me, but Zamp confirmed that this was a good reading for my AGM 12V battery. At some point, I plan to add a roof mounted panel as well since I am often worried that the portable version may decide to walk off sometime when I am parked at a trailhead even with a long steel cable and lock run through the portable panel legs. Anyone care to critique or comment about this routine?

 

[Vic Harder]

If you look at the datasheet for your chargers, it might tell you what you will see on a voltmeter when it is going through the various charge stages. I use a Victron, - Datasheet - which has fully customizable voltage levels, but the default for AGM is 13.8v at float. That is pretty typical for AGM chargers. During charging, (absorption mode) the voltage is 14.4V on my Victron by default.

And if the batteries sit for a day or so without being plugged into anything (no charger, no loads - FWC kill switch activated) then 12.8 is where AGM batteries settle.

All of this this said, using voltage is a lousy way to determine battery State of Charge (SOC). That's because under load the battery voltage level drops, and it takes time (hours) to "settle". You really need to get some kind of shunt based battery meter. I like the Victron 712 BMV but it is pricey. There are Chinese knock-offs that are supposedly OK too.

 

[Outnabout]

If you look at the datasheet for your chargers, it might tell you what you will see on a voltmeter when it is going through the various charge stages. I use a Victron, - Datasheet - which has fully customizable voltage levels, but the default for AGM is 13.8v at float. That is pretty typical for AGM chargers. During charging, (absorption mode) the voltage is 14.4V on my Victron by default.

And if the batteries sit for a day or so without being plugged into anything (no charger, no loads - FWC kill switch activated) then 12.8 is where AGM batteries settle.

All of this this said, using voltage is a lousy way to determine battery State of Charge (SOC). That's because under load the battery voltage level drops, and it takes time (hours) to "settle". You really need to get some kind of shunt based battery meter. I like the Victron 712 BMV but it is pricey. There are Chinese knock-offs that are supposedly OK too.

If the batteries are connected in parallel do you only need to connect one of the batteries to the monitor?

 

[Vic Harder]

yes.... just the one - which is really two.

 

[Outnabout]

yes.... just the one - which is really two.

Thanks, that what I thought. Cheers