# What should a AGM deep cycle battery resting voltage be ?



## 4179Brad (Mar 23, 2017)

So I just bought a rebranded Northstar 24f from batteries plus (X2 Battery) and it was at 12.7 when checked with multimeter before putting it in my car . Now after running then shutting the car off it goes down to 12.6 sometimes 12.5 ... I thought deep cycle agm batteries were supposed to rest closer to 13v ? Should I bring this battery back ?


----------



## muzikmanwi (Dec 25, 2014)

My Odyssey at shut off is 13.1 volts and it drops down to 12.7 volts within about 1/2 hour.


----------



## gijoe (Mar 25, 2008)

12.6, it's 6 x 2.1 v cells.


----------



## nineball76 (Mar 13, 2010)

Alternators also don't fully charge a battery. typical;ly an agm needs to be charged 14.5-14.9v absorption. Also depends on how long you drive the vehicle. It typically takes 30 minutes to restore the lost energy from what the starter pulls. if you're only driving the car down to the store 3 blocks away everyday, eventually that battery won't hold much more than 12.2-12.3v.


----------



## 4179Brad (Mar 23, 2017)

so should I get a charger and do a 3 stage charge to it ? I read somewhere that to charge to full capacity you need to first discharge and then charge with a 3 stage charger with a agm setting .. otherwise it will never reach its full potential .. anyone know more about that ? I just bought an expensive battery for a reason and I want to get its maximum potential not 85% etc


----------



## nineball76 (Mar 13, 2010)

4179Brad said:


> so should I get a charger and do a 3 stage charge to it ? I read somewhere that to charge to full capacity you need to first discharge and then charge with a 3 stage charger with a agm setting .. otherwise it will never reach its full potential .. anyone know more about that ? I just bought an expensive battery for a reason and I want to get its maximum potential not 85% etc


check out ctek chargers. I just bought a ctek mus25000, 25a 8 stage charger, power supply, and reconditioner.


----------



## Rocketjones (Oct 23, 2008)

Depending on your car's make, you can run a diode mod to increase voltage.


----------



## Marky (Nov 15, 2011)

Charging a AGM above 14.5 volts is death to its longevity. A AGM battery should have the voltage regulator matched for a AGM battery!
I bought a DC Power 8307-270-XP alternator that is equipped with the proper AGM regulator which tops out at 14.3 volts. Its a 270 amp unit and my batteries are 4 years old now and strong as hell. I bought Die Hard Platinum's and they came with a 4 year free replacement warranty and pro-rate out to 84 months. As long as you have the proper charge system in vehicle. Sears no longer sells that battery tho lol.....
Just throwing a AGM battery in a older car not designed for the AGM will end in short battery life. It's a fact and I know what I'm talking about......


----------



## Alrojoca (Oct 5, 2012)

X2 having to drive it for at least 25 mins constantly, and usually at 61 mph, depending on the car manufacturer, you can learn all the dirty tricks if you get a voltage display to learn and know the behavior of your charging system, every manufacturer will have a different smart charging system, most charging systems in city driving and cars post 2005 as far as I know may keep the voltage under 12.8 volts while driving after the first initial 4 mins of driving it, again it depends on the car manufacturer, idle or stopped is an exception to the 12.7 volt display. 
The Best thing you can do, if you drive less than 20 mins every day figure out a combination of things that will keep your voltage at 14-14.4, some cars keeping the air blower on, and parking light on, or simply by turning the head lights on every time, it will keep the voltage above 13.75 volts and under 14.4.

Smart chargers like the Beltran or citek will help a bit but also will not fully charge it to the point to notice a 12.7 volt 24 hr resting voltage.

All newer cars with their ecm's factory alarms etc, pretty much will show a resting voltage of 12.3-12.4 after 36 hrs of resting voltage due to the parasitic voltage drop.

Again there might be some exceptions depending on the car manufacturer, and most of them do not know a system with 4 amplifiers is being used since it's not smart enough to know the owner installed a high current draw audio system.


----------



## undone1 (Sep 30, 2008)

Marky said:


> Charging a AGM above 14.5 volts is death to its longevity. A AGM battery should have the voltage regulator matched for a AGM battery!
> I bought a DC Power 8307-270-XP alternator that is equipped with the proper AGM regulator which tops out at 14.3 volts. Its a 270 amp unit and my batteries are 4 years old now and strong as hell. I bought Die Hard Platinum's and they came with a 4 year free replacement warranty and pro-rate out to 84 months. As long as you have the proper charge system in vehicle. Sears no longer sells that battery tho lol.....
> Just throwing a AGM battery in a older car not designed for the AGM will end in short battery life. It's a fact and I know what I'm talking about......


depends on how old and what make the car/truck is...most older vehicles charge at or around mid 13's to maybe 14ish when hot..


----------



## undone1 (Sep 30, 2008)

Alrojoca said:


> X2 having to drive it for at least 25 mins constantly, and usually at 61 mph, depending on the car manufacturer, you can learn all the dirty tricks if you get a voltage display to learn and know the behavior of your charging system, every manufacturer will have a different smart charging system, most charging systems in city driving and cars post 2005 as far as I know may keep the voltage under 12.8 volts while driving after the first initial 4 mins of driving it, again it depends on the car manufacturer, idle or stopped is an exception to the 12.7 volt display.
> The Best thing you can do, if you drive less than 20 mins every day figure out a combination of things that will keep your voltage at 14-14.4, some cars keeping the air blower on, and parking light on, or simply by turning the head lights on every time, it will keep the voltage above 13.75 volts and under 14.4.
> 
> Smart chargers like the Beltran or citek will help a bit but also will not fully charge it to the point to notice a 12.7 volt 24 hr resting voltage.
> ...


use the Pulsetech myself.. batteries are still sitting at 12.7-12.8 resting after 2 months......all else is spot on..


----------



## Alrojoca (Oct 5, 2012)

If it's not going to be driven for a week a smart charger will help for sure, but in between 2 or 3 days using one when the car is driven 20 mins or less per day, it may extend the battery life, but still not fully charge it as if it is driven for 25-30 min at a 14-14.4 volt alternator charge.

Also sulfation takes place below 11.5 volts, if the battery is old, some sulfation removal can help, if that northstar battery holds 12.5 V with a newer car after 36 hr resting voltage then it is good and there is nothing to worry about in my opinion


----------



## nineball76 (Mar 13, 2010)

undone1 said:


> use the Pulsetech myself.. batteries are still sitting at 12.7-12.8 resting after 2 months......all else is spot on..


I top off several agm (xs d7500, Juicebox black cherry, Odyssey pc2150s) several times a year and they rest on my bench 12.9-13.1.


----------



## Alrojoca (Oct 5, 2012)

nineball76 said:


> I top off several agm (xs d7500, Juicebox black cherry, Odyssey pc2150s) several times a year and they rest on my bench 12.9-13.1.



I agree that Resting voltage being disconnected is totally different than when it's connected to the car, the 12.5V reading after not starting or driving the car for over 12 hrs is totally normal, in some cars it may be close to 13 V, there is an non avoidable parasitic draw with some newer cars apparently after 24 hrs, it it may be possible that after 2 weeks the voltage for that northstar battery may still be around 12.5V or only drop 0.1 volt per week while connected to a newer vehicle and not driven or the engine started within that time.

Funny but I searched and searched, and there is no defined time frame of what can be called resting voltage, I read someone said 3-4 hrs, but I think it's more like 18, it's an interesting topic, just like a fully charged battery should be at 12.7V, does that mean that if it drops to 12.3V after 18 hrs it is bad? 
Not it is simply the parasitic draw. 

Maybe some home smart chargers top off the charge better than others, I have just top off mine and check it after 24 hrs without driving it, and it shows a very average slightly higher voltage than if I drove the car for 15 min the day before, but if I drive it for a constant 30 mins one day on the highway above 61 mph the voltage shown after 24 hrs is higher than the one that the smart charger supplied.


----------



## nineball76 (Mar 13, 2010)

Alrojoca said:


> I agree that Resting voltage being disconnected is totally different than when it's connected to the car, the 12.5V reading after not starting or driving the car for over 12 hrs is totally normal, in some cars it may be close to 13 V, there is an non avoidable parasitic draw with some newer cars apparently after 24 hrs, it it may be possible that after 2 weeks the voltage for that northstar battery may still be around 12.5V or only drop 0.1 volt per week while connected to a newer vehicle and not driven or the engine started within that time.
> 
> Funny but I searched and searched, and there is no defined time frame of what can be called resting voltage, I read someone said 3-4 hrs, but I think it's more like 18, it's an interesting topic, just like a fully charged battery should be at 12.7V, does that mean that if it drops to 12.3V after 18 hrs it is bad?
> Not it is simply the parasitic draw.
> ...


A car should have less than .5a parasitic draw, most are closer to .2a. Shouldn't dip more than .2-.3v over even a week with a good agm.


----------



## nineball76 (Mar 13, 2010)

Odyssey and Northstar have seen 12.9 rest, accessories on drawn down to 12.5, turned accessories off and bounced right back to 12.8


----------



## Alrojoca (Oct 5, 2012)

Obviously North Star AGM batteries are different animals than standard batteries and the price difference is for a reason.

The op should simply drive the car for over 25 mins on the highway and check it after 12-18 hrs and again 12 or 24 hrs after that.

The car electronics, may demand more or even try to monitor a voltage range, despite if northstar fights to keep the voltage at 12.8 volts, it may be beyond control, cars these days, may be like computers, doing their things, even when they are shut down as long as the laptop battery is connected , it can do things without us knowing it. Again it depends on the the car brand, they all regulate consumption in different ways. 

If northstar says, it's bad then it should be replaced and hope the voltage stays at 12.7. 

The easiest thing to do, take it out or disconnect it from the car and check it 12 hrs later after it was charged or the car driven for while


----------

