Charging AGM Batteries

faucet1 wrote:
Yes, John, that is essentially my charger. Except it doesn't have the "C". I purchased my charger from Sams some time in the late nineties. The manual reads almost the same, and the "Personal Precautions" reads word for word including "For Lead Acid Only". I suppose that wording is/was my concern. Since I only have one of the small AGM batteries in my possession at the current time I'm going to try a test charge to see what the results might be. Again, thanks to everyone for your interest and comments. If I blow the battery up, I will post the results.

Uhhh, AGMs are lead-acid!, as are Gels and flooded.

The difference is mainly in the acid. The cautions against high Volts are related to the sealed, or valve regulated ones.

Flooded can be open or sealed, but the acid is a free flowing liquid solution and the battery must always be upright to keep the acid in contact with the plates.

AGMs and Gels are always sealed where the acid is immobilized and they can be placed on their side or end.

HTH;
John

Yes, John, that is essentially my charger. Except it doesn't have the "C". I purchased my charger from Sams some time in the late nineties. The manual reads almost the same, and the "Personal Precautions" reads word for word including "For Lead Acid Only". I suppose that wording is/was my concern. Since I only have one of the small AGM batteries in my possession at the current time I'm going to try a test charge to see what the results might be. Again, thanks to everyone for your interest and comments. If I blow the battery up, I will post the results.

PNichols, great advice on over complicated maintenance. IMO, it sounds more complicated than it is. Once you figure it out, it's simple. You won't get sulfation while they're being charged. BUT that voltage in the summer might open the vents so it's still a good idea to disconnect them or hook them up to a temp compensated charger. As you already know, self discharge is so low that leaving them unconnected in the summer is not really a big deal. Although mine would be on a float charge 24/7. :)

faucet1 wrote:
This is great material. And I am considering the AGM's to replace my 4-6 volt batteries in the not too distant future. But, first...the reason for my question about using a Century 87151 automatic charger at the low 2 amp setting is....let's say you wanted to recharge a simple kids electric scooter AGM 12 volt 7 amp-hour battery. I know this is a far cry from trying to figure out how, etc, to recharge a 4 battery 800 + amp-hour system, but if we can understand a simple small battery recharge it may shed some additional light on charging the more expansive systems. and let's assume the physical makeup of the small battery is the same as the 200+ AH. This may be a mute point in that as I understand the previous discussions that my charger even at the 2 amp setting may put out too much voltage. Am I understanding this correctly, and subsequently shorten the life of any AGM?

Is this the Charger?

Is this the manual?

If so, on page 6, I recommend you:

Step1 - Normal/Automotive
Step2 - Charge
Step3 - 2A

Then:
Attach cables
Plug in charger

HTH;
John

bdosborn wrote:
Does anyone have any information of what happens of you don't follow the recommened batery charging setpoints for an AGM? Do I cut my battery life in half? Does it blow up in the middle of the night? How do you test the battery for SOC and verify that the factory recommended charge setpoints are actually the best?

I'm the odd man out here battery-maintenance-wise, but have had very good luck with my battery maintenance routine.

We have had the same two 12V 100AH wheelchair AGM batteries in our motorhome for 7 years and they're still going strong. When the MH engine is running, these two AGMs are connected in direct parallel (via a heavy duty solenoid using silver alloy contacts) with the main wet cell chassis engine and the alternator. The chassis battery is about 5 years old.

When in storage during fall/winter/spring the AGMs get ~13.6-13.7 volts from our stock fixed voltage MH converter continuously. The chassis engine battery is continuously hooked up to a small multi-stage maintenance charger. During the summer when in storage the AGMs are disconnected from any charger much of the time so as to keep sulphation from being introduced by seeing a constant ~13.6-13.7 volts from the converter too long in warmer weather. The chassis wet cell battery remains constantly hooked up to the little multi-stage maintenance charger during the summer, too.

However, my batteries never sit much in a state of less than full charge and my AGMs are unusual in that they are wheelchair batteries that require floating at 13.5-13.8 volts - not 13.2 volts - so the fixed voltage converter does not harm them.

We don't drycamp longer than about 5 days at a stretch, so we merely hit the AGMs with some 14.X alternator volts once in awhile by idling the main engine for a bit and then following it up with 4-5 hours of converter voltage powered by a very small and quiet Honda generator - no solar. We can get by as much as around 3 days without idling the main engine or using the little Honda. We do keep the propane furnace cycling around 60-65 degrees all night most nights, too ... as well as using a no-heat no-steam CPAP machine every night. We have all LED lighting.

This simple system has worked well. Sometimes I think many RV folks make the whole battery maintenance thing too complicated. Just keep them always charged fully during extended storage without over-charing them and watch the charging time versus voltage in hot weather so as to keep from boiling them - or in the case of AGMs - to keep from vaporizing the water (which cannot be replaced) out of their one-way valves.

This is great material. And I am considering the AGM's to replace my 4-6 volt batteries in the not too distant future. But, first...the reason for my question about using a Century 87151 automatic charger at the low 2 amp setting is....let's say you wanted to recharge a simple kids electric scooter AGM 12 volt 7 amp-hour battery. I know this is a far cry from trying to figure out how, etc, to recharge a 4 battery 800 + amp-hour system, but if we can understand a simple small battery recharge it may shed some additional light on charging the more expansive systems. and let's assume the physical makeup of the small battery is the same as the 200+ AH. This may be a mute point in that as I understand the previous discussions that my charger even at the 2 amp setting may put out too much voltage. Am I understanding this correctly, and subsequently shorten the life of any AGM?

faucet1 wrote:
I was looking for info on trying to charge, recharge AGM Batteries. If a convenional automatic charger is set to the deep cycle 2 amp setting, will this over charge the AGM Battery? Constructive comments would be appreciated. I did a query on charging agm batteries but didn't see any posts.
Thanks
David

I have Fullriver AGM 110 amhr and it takes about an hour to recharge to 100% capacity,when 20% down,,using 10 to 15 amp setings,havent tried 2 amp as Im always in a hurry, :)
but dont see why it should overcharge it IF you have proper three stage automatic charger.
I use Nautilus inteligent charger which has settings for regular,gells and AGM batts..

I also use my 80w solar panel and it takes about 4 - 5 hrs as that is very low trickle charge..
hope that helps

landyacht318 wrote:
In regards to the recommendations of battery manufacturers for charging their batteries, I am usually not even able to meet the minimum recommended charge current requirements for my flooded DC Crowns at 12 to 18 amps per 100 A/h of battery and certainly not the 40 amps recommended by Odyssey

I have to be honest that while I can and do occasionally plug into the grid for charging, and my alternator is highly capable except when hot at idle speeds, that my 198 watts of solar is by far doing the majority of my recharging. At least I can control the solar voltage setpoints, but 198 watts seems to fall well short of what is recommended, by about 300 to 500 watts.

If one looks only at the total number of amp hours returned, I am fully charging them most days, but if one looks at the recommended minimum bulk charging recommendations and compares them to the maximum of what my solar can do, I am well below. While I point to my lack of watering on time as the reason I only get 2 years out of a pair of daily cycled quality deep cycles, perhaps it is more my lack of Bulk amps to feed them that is just as responsible for their shorter than expected and hoped for lifespans.

I too wonder if less overall capacity will allow me to come closer to reach the minimum recommended bulk current. Sure the smaller batteries will be cycled deeper in the same use, but will the higher relative bulk charging capacity be better for the batteries and allow them to last longer despite the deeper daily cycling?

So I cannot meet their specifications without plugging in more often and also acquiring a bigger charger/converter. More solar is not going to happen. More Driving is not gonna happen intentionally, just for this purpose. I am not going to ever get a generator and listen to that stinkbox. Solar will remain my main recharging source, and no more can fit on my roof without completely starting over. Not gonna happen.

So as for me getting AGM's, which by and for the most part recommend much higher bulk current requirements than my floodeds at twice the price or more, well, they have to last at least twice as long and more for the same ROI given the same dis and recharging regimen. The warm and fuzzies of having high Dollar AGM's will wear off quick. I'd rather have 350$ more in my pocket the day after purchase if there is no guarantee they are going to last twice as long.

I have no indications that they can do this. A few reports by those who cycle their AGM batteries a few times a year for several years and that they are good as ever are not pertinent to me who cycles daily and apparently recharges inadequately. Can AGM's tolerate a regular bulk current in the 1/4 range of recommended for twice as long as my Flooded DC's which have been fed nearly half or less the recommended bulk current.

Am I overthinking this? Of course. Many of the regulars replying here in this forum are overthinking things regarding batteries, and occasionally someone steps back and just says
'why bother overthinking things? It works fine, will work fine, it's not rocket science with huge consequences of failure...carry on.'

I understand this, I am even guilty of it several years back when BFL13 started experimenting a LOT and posting results and charts for us all to digest and ponder and discuss, all in an attempt to better understand for which we all should be thankful.

I enjoy intelligent discourse on these topics and wish I understood more. I really wish the affordable charging sources marketed to people like us had adjustable voltage setpoints and temperature compensation as standard, instead of the 'trust us, we know best" algorithm that is at odds with the manufacturer's recommendations a lot of the time. Some want to set it and forget it, others want precise control because that is the way their mind works.

Perhaps the set it and forget it guys should ask which products allow them this luxury, and leave the anal retentive worry worts like us to hash it all out.

I will be acquiring new batteries very soon. Perhaps my engine battery will be a high CCA AGM that is rarely cycled and does not even need the .4c bulk charging current, but it is looking like my 2 house batteries are going to be Crown, Trojan or US Battery flooded group 27's, as group 31's will not fit. I will just have to be more vigilant on the watering.


I happen to find the different manufacturer's charging recommendations interesting, and will make no apologies for posting links to them even if they might be somewhat at odds with our resident battery Engineer and his seemingly deliberately obtuse replies, however humorous and enlightening they can be, if one reads them enough times and understands his background.

No offense Intended Mex. Please don't stop contributing. I'd like your opinions as to why these manufacturer recommendations vary as much as they do, supposing they are not mutilated by the accountants and marketers before they are allowed to be seen.

And for those interested, here are the US Battery charging recommendations for both flooded and AGM linked to me earlier by one of their representatives.

http://www.usbattery.com/usb_images/charging_instruction_2011_3.pdf

landyacht318

I think that you are noticing the difference between service charging at higher voltages compared to constant charging in permanent system.
I remember a golf cart supplier DE sulfating batteries by loading them with huge draw. They had an element the size of a toaster glowing white hot. This is brutal service was designed to mechanically temp shock the plates. This is ok in an industrial environment. RV’s and solar are not like this.
The charging methods are just different. Don't mix the voltage values between them. 14.4v bulk charge on an AGM is fine if you are not temp compensating. The charge times will only be a little longer.
I am in the set it and forget it crowd. The modern 3 and 4 stage controllers are very good.
MM49

landyacht318 wrote:

Am I overthinking this? Of course. Many of the regulars replying here in this forum are overthinking things regarding batteries, and occasionally someone steps back and just says
'why bother overthinking things? It works fine, will work fine, it's not rocket science with huge consequences of failure...carry on.'

I find that I have less total niggling problems in my life by spending a little time "overthinking" things. Example, there are many thousands of campers that don't mind going to the gas station to fill up gas cans for their generators before each and every trip. Nor, while they are on their trip, filling up their gennys at the required times. I see that as a supreme hassle and a waste of my off time. So, I "overthink" my setup and spend too much money just so I can sit on the beach all day without needing to move one muscle unless I want to. Even when I'm at home my setup allows me to spend VERY little of my time in maintenance. Even adding water only occurs ONCE a year (once in the spring before it gets hot). A little "overthinking" = a LOT of not thinking. YMMV.

In regards to the recommendations of battery manufacturers for charging their batteries, I am usually not even able to meet the minimum recommended charge current requirements for my flooded DC Crowns at 12 to 18 amps per 100 A/h of battery and certainly not the 40 amps recommended by Odyssey

I have to be honest that while I can and do occasionally plug into the grid for charging, and my alternator is highly capable except when hot at idle speeds, that my 198 watts of solar is by far doing the majority of my recharging. At least I can control the solar voltage setpoints, but 198 watts seems to fall well short of what is recommended, by about 300 to 500 watts.

If one looks only at the total number of amp hours returned, I am fully charging them most days, but if one looks at the recommended minimum bulk charging recommendations and compares them to the maximum of what my solar can do, I am well below. While I point to my lack of watering on time as the reason I only get 2 years out of a pair of daily cycled quality deep cycles, perhaps it is more my lack of Bulk amps to feed them that is just as responsible for their shorter than expected and hoped for lifespans.

I too wonder if less overall capacity will allow me to come closer to reach the minimum recommended bulk current. Sure the smaller batteries will be cycled deeper in the same use, but will the higher relative bulk charging capacity be better for the batteries and allow them to last longer despite the deeper daily cycling?

So I cannot meet their specifications without plugging in more often and also acquiring a bigger charger/converter. More solar is not going to happen. More Driving is not gonna happen intentionally, just for this purpose. I am not going to ever get a generator and listen to that stinkbox. Solar will remain my main recharging source, and no more can fit on my roof without completely starting over. Not gonna happen.

So as for me getting AGM's, which by and for the most part recommend much higher bulk current requirements than my floodeds at twice the price or more, well, they have to last at least twice as long and more for the same ROI given the same dis and recharging regimen. The warm and fuzzies of having high Dollar AGM's will wear off quick. I'd rather have 350$ more in my pocket the day after purchase if there is no guarantee they are going to last twice as long.

I have no indications that they can do this. A few reports by those who cycle their AGM batteries a few times a year for several years and that they are good as ever are not pertinent to me who cycles daily and apparently recharges inadequately. Can AGM's tolerate a regular bulk current in the 1/4 range of recommended for twice as long as my Flooded DC's which have been fed nearly half or less the recommended bulk current.

Am I overthinking this? Of course. Many of the regulars replying here in this forum are overthinking things regarding batteries, and occasionally someone steps back and just says
'why bother overthinking things? It works fine, will work fine, it's not rocket science with huge consequences of failure...carry on.'

I understand this, I am even guilty of it several years back when BFL13 started experimenting a LOT and posting results and charts for us all to digest and ponder and discuss, all in an attempt to better understand for which we all should be thankful.

I enjoy intelligent discourse on these topics and wish I understood more. I really wish the affordable charging sources marketed to people like us had adjustable voltage setpoints and temperature compensation as standard, instead of the 'trust us, we know best" algorithm that is at odds with the manufacturer's recommendations a lot of the time. Some want to set it and forget it, others want precise control because that is the way their mind works.

Perhaps the set it and forget it guys should ask which products allow them this luxury, and leave the anal retentive worry worts like us to hash it all out.

I will be acquiring new batteries very soon. Perhaps my engine battery will be a high CCA AGM that is rarely cycled and does not even need the .4c bulk charging current, but it is looking like my 2 house batteries are going to be Crown, Trojan or US Battery flooded group 27's, as group 31's will not fit. I will just have to be more vigilant on the watering.


I happen to find the different manufacturer's charging recommendations interesting, and will make no apologies for posting links to them even if they might be somewhat at odds with our resident battery Engineer and his seemingly deliberately obtuse replies, however humorous and enlightening they can be, if one reads them enough times and understands his background.

No offense Intended Mex. Please don't stop contributing. I'd like your opinions as to why these manufacturer recommendations vary as much as they do, supposing they are not mutilated by the accountants and marketers before they are allowed to be seen.

And for those interested, here are the US Battery charging recommendations for both flooded and AGM linked to me earlier by one of their representatives.

http://www.usbattery.com/usb_images/charging_instruction_2011_3.pdf