AGM car batteries.




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  1. #1
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    Default AGM car batteries.

    I don't understand that some vehicles uses AGM batteries as primary batteries but you cannot connect a AGM battery through a solenoid as a secondary battery to run a fridge as it will boil it [apparently].Does the BMW's and Mercs have a different alternator or charging system to charge a AGM safely? So this also means if my battery in my Hilux say goodbye I canít replace the battery with a AGM because my alternator cannot charge it.
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    Default Re: AGM car batteries.

    I have an AGM battery in my 2005 hilux for about a year now and everything seems fine......(as a crank battery)
    Put in by battery centre so I assume they know what they are doing.

    However checked the water levels the other day and they were low (3months ago) filled up and no movement since then.

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    Default Re: AGM car batteries.

    Quote Originally Posted by Lofty View Post
    I don't understand that some vehicles uses AGM batteries as primary batteries but you cannot connect a AGM battery through a solenoid as a secondary battery to run a fridge as it will boil it [apparently].Does the BMW's and Mercs have a different alternator or charging system to charge a AGM safely? So this also means if my battery in my Hilux say goodbye I canít replace the battery with a AGM because my alternator cannot charge it.
    Where do you get the AGM batteries cant be charged by alternators? I have read that these batteries are used extensively in the US in RVs, using "smart isolators", and that they are happy with a cars voltage of 14.2-14.4V. Certainly when I charge my AGM battery in the trailer with a smart charger on AGM mode, the NL monitor complains about overcharging condition.
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    Default Re: AGM car batteries.

    Quote Originally Posted by Ingetrap View Post
    I have an AGM battery in my 2005 hilux for about a year now and everything seems fine......(as a crank battery)
    Put in by battery centre so I assume they know what they are doing.

    However checked the water levels the other day and they were low (3months ago) filled up and no movement since then.
    Something about this seems wrong.

    Under the impression AGM batteries are sealed.

    Maybe pic of battery

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    Default Re: AGM car batteries.

    Quote Originally Posted by Prof View Post
    Under the impression AGM batteries are sealed.
    Definately

    https://batteryuniversity.com/learn/..._glass_mat_agm

    I do note this however, relating to the OPs question

    " Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell); a direct replacement with a sealed unit could overcharge the battery on a long drive. "

    So it seems the float voltage is the problem.
    Last edited by SimonB; 2018/10/10 at 08:17 AM.
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  7. #6
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    Default Re: AGM car batteries.

    The reason why I asked is I want to go this route but my old deepfycle is almost past his date and them I want to replace it with a AGM.
    Quite a few posts in the last few week suggest that a normal solenoid system is going to cook the AGM and I dont want a R4000 doorstop.
    Last edited by Lofty; 2018/10/10 at 12:58 PM.
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    Default Re: AGM car batteries.

    Quote Originally Posted by Lofty View Post
    The reason why I asked is I want to go this route but my old deepfycle is almost past his date and them I want to replace it with a AGM.
    Quite a few posts in the last few week suggest that a normal solenoid system is going to cook the AGM and I dont want a R4000 doorstop.
    I would suggest you need to investigate how your specific vehicle charges. Being a 2017 perhaps its alternator is a little more intelligent. I don't know, or look at a DC/DC charging system
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    Default Re: AGM car batteries.

    Quote Originally Posted by SimonB View Post
    I would suggest you need to investigate how your specific vehicle charges. Being a 2017 perhaps its alternator is a little more intelligent. I don't know, or look at a DC/DC charging system
    No its not an intelligent alternator according to the internet and the clever people,I measured it at 14.1 V
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  11. #9
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    Default Re: AGM car batteries.

    According to this link you need and isolator to stop the charge from the alternator to the AGM battery to prevent damage.




    https://www.batterystuff.com/kb/arti...ry-basics.html
    Last edited by Lofty; 2018/10/14 at 04:36 PM.
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  12. #10
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    Default Re: AGM car batteries.

    I am confused. The National Luna website has a very informative article about charging second batteries-solenoid vs DC-DC chargers (DC and Solar dual) and I saw nothing about AGM batteries boiling.

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    Default Re: AGM car batteries.

    Quote Originally Posted by Lofty View Post
    According to this link you need and isolator to stop the charge from the alternator to the AGM battery to prevent damage.


    https://www.batterystuff.com/kb/arti...ry-basics.html
    You are likely referring to the following comment:
    BatteryStuff Tech: We recommend that you use a Battery Isolator when charging through the alternator so you donít overcharge a battery. They are designed to charge not only the caravanís battery in your case, but an additional battery pack. The key thing you need to know with isolators is that you need to match the chemistry so that it knows how to charge the battery correctly. Another words if you have an AGM battery for your house battery, then you should have an AGM under the hood as well. This will ensure the isolator charges the batteries correctly and doesnít overcharge the battery. I have heard of isolators that can determine the charge if chemistry doesnít match, but they are extremely expensive, and Iím not sure how reliable they really are. It is best to just match chemistry in my opinion. (April 26, 2016)

    I would not worry about the above comment - it is someone's opinion and not gospel.

    RV application is not like solar where you really want to get the max out of your system that cycles each and every day.
    We all mix and match according to what we have and what we can afford - and it works surprisingly well most of the time.
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  14. #12
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    Default Re: AGM car batteries.

    Quote Originally Posted by Eggie View Post
    You are likely referring to the following comment:
    BatteryStuff Tech: We recommend that you use a Battery Isolator when charging through the alternator so you don’t overcharge a battery. They are designed to charge not only the caravan’s battery in your case, but an additional battery pack. The key thing you need to know with isolators is that you need to match the chemistry so that it knows how to charge the battery correctly. Another words if you have an AGM battery for your house battery, then you should have an AGM under the hood as well. This will ensure the isolator charges the batteries correctly and doesn’t overcharge the battery. I have heard of isolators that can determine the charge if chemistry doesn’t match, but they are extremely expensive, and I’m not sure how reliable they really are. It is best to just match chemistry in my opinion. (April 26, 2016)

    I would not worry about the above comment - it is someone's opinion and not gospel.

    RV application is not like solar where you really want to get the max out of your system that cycles each and every day.
    We all mix and match according to what we have and what we can afford - and it works surprisingly well most of the time.
    Exactly. Some of these websites have terrible information enshrined in a supposedly credible cloak.

    Even batteryuniversity.com has some VERY dicey information and advise. There is a foundation of scientific fact smothered in urban legends.
    Last edited by Fluffy; 2018/11/02 at 04:13 PM.
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  16. #13
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    Default Re: AGM car batteries.

    Quote Originally Posted by Eggie View Post
    You are likely referring to the following comment:
    [I][COLOR=#000080] Another words if you have an AGM battery for your house battery, then you should have an AGM under the hood as well.
    Two AGM batteries ? Then I will rather go DC-DC route.How is the Varta AGM batteries?
    Last edited by Lofty; 2018/11/06 at 02:31 AM.
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  17. #14
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    Default Re: AGM car batteries.

    Most alternators I have dealt with boost charge at ~ 14.5V and floats at ~13.8 V once the current amperage tapers off / battery gets full

    If the event that the primary (starter) battery is fresh and the secondary (AGM) battery is run down over night powering the fridge overnight, as the CTEK 250 or National Luna solinoid kept them disconnected while the engine is off.....Upon starting the car the next morning the CTEK, solinoid will reconnect the batteries. The AGM battery will be low voltage(~ < 13 V) and the primary battery will be higher voltage ( ~ 13.5V). The alternator will then start to charge both batteries at max available current depending on engine rpm. The parallel connected batteries will try to equalize in voltage with a very depleted AGM in fact drawing additional charge from the primary battery.

    This will continue untill both the primary battery and starter battery is equilized at the same voltage after which the alternator will charge and raise the voltage together on both batteries at the boost voltage of about 14.5 V depending on current draw and engine rpm.

    Once the batteries reach full state of charge or the change over current threshold the charging voltage will change over to the float charge voltage of about 13.8V.

    AGM batteries are supposed to be "super hero" lead acid batteries. They only feature lead plates placed in acid drenched fiber glass mat "socks" instead of naked lead plates sitting in an acid tank. The "socks" helps to support the cell plates from loosing their lead paste. ( dropping worthless to the bottom of the battery and causing battery degradation)

    As they run on lead acid battery chemistry I don't see why need different voltages.

    Because they can be cycled to a greater extent AGM batteries are used in the cars equipped with idle stop/start features and sometimes they are not charged on purpose in order provide "charging space " for regenerative charging via "intelligent alternator control" ( battery is only charged when you apply the brake or when the car is free wheeling) in order to charge the car for "free" and make the car more economical
    Last edited by vlakkie; 2018/11/13 at 10:56 PM.
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