Home Battery Charger for AGM Batts?

[lvictorlucas]

Don't fall for the marketing BS. First not all AGMs are the same, not even if they are from the same manufacturer. It depends on the specific model of battery. All cheap battery chargers with AGM settings are not really for charging AGM batteries but some mode a Chinese marketeer added because it sounded good. Obviously any "automatic" or non programmable charger cannot be designed for AGM batteries as it depends on the specific chemistry of that particular model. By programmable I do not mean just one with a battery temperature sensor and a couple of parameters such as voltage, current and time settings. If you want a real AGM charger there is only one cost effective solution which is to design it yourself using something like an Arduino. Rebranders of AGMs have no idea how to charge them as they go with the cheapest manufacturer for each lot purchase. To get the data you need you have to talk to the battery chemist at the real manufacturer for you model. Don't even think customer service knows anything about charging the batteries or he would be making ten times as much. I have thought about selling one myself but no one does it because it takes a lot of effort to get the real data for the specific model then requires the user to enter the data. The market is just not there so no one does it.

[john61ct]

No one should buy the lousy quality AGMs you're talking about for true deep cycling.

The half-dozen or so quality makers in NA market publish detailed manuals, spec sheets and have well qualified technical support on call to answer questions.

Dozens of chargers are perfectly fine for the OP use case, and available for well under $300.

For not much more, marine quality user-custom programmable ones are available at high amperages for use in deep cycling mode.

A DIY science project programming an Arduino is not an appropriate suggestion for ordinary sailors.

[hamburking]

1) Batteries on a cement floor will lose their charge quickly. I don't know the science, but I believe its true.

2) An automotive battery charger differs from a marine charger in that it actually has a small current draw when not charging. So if you leave it connected to the battery, and not plugged in (to the wall), your batteries will drain fairly quickly. This happened to me. Personal experience.

3) Batteries are heavy. New batteries cost less than a new back.

[john61ct]

Originally Posted by hamburking

Batteries on a cement floor will lose their charge quickly. I don't know the science, but I believe its true.

May have been true pre-war, but has been an urban myth for at least 70 years.

[GordMay]

Originally Posted by john61ct

May have been true pre-war, but has been an urban myth for at least 70 years.

INDEED!

[Mr B]

Update on my El Cheapo Chinese Intelligent Pulse Battery charger, $36-00
It has 110 and 240 volt plugs, So can be plugged into either,

One lead acid battery is fully charged and has held the full charge for a week, Its been dead for 7 years,
One AGM is fully charged and has held a full charge for a week. It was dead and has been sitting under my bench for at least 15 years,

The 8D lead acid has been siting on a steel tray out in the weather for 5 years,
It was dead, Its now got 7 volts in it, But is still on the charger,
I will see what its like in a week or so, Big batterys take a few days to charge up,
They are all sitting on a concrete floor, They did change the cases years ago,
So sitting on concrete no longer effects them now,

Scam, Hokus Pockus or whatever, The two batterys that have been brought back to full life has definately paid for my charger,

Im more than pleased with it, Im actually Impressed with it,

Cheers Brian,

[john61ct]

Do a capacity test to see, holding a charge does not mean usable in reality.

A charger good for bringing a battery "back from the dead" may not be ideal for regular use deep cycling.

Which in turn is different from maintaining a Starter battery.

[lvictorlucas]

It will be very interesting when you do a load test that discharges them down to 50% or so. Almost any battery can be brought up to 13 volts or so if it doesn't have a shorted cell. The only way to actually test them is to take them down to 50% of the rated energy.

[Nicholson58]

Originally Posted by Sailon1

Thanks, Chris, and I should have mentioned that I have no electrical
connection near the boat when it's on the cradle.

I also stored on the boat. The yard does not allow winter connections. I removed the battery negative. Hardly any loss all winter.

Home chargers don’t usually have float. You could damage batteries if you are not careful.

[a64pilot]

The self discharge rate for a quality AGM battery is very low, if disconnected and left on the boat they will be fine.
I would take them home though if extremely cold conditions were expected.
Lifeline’s take on storage

[Mr B]

Originally Posted by john61ct

Do a capacity test to see, holding a charge does not mean usable in reality.

A charger good for bringing a battery "back from the dead" may not be ideal for regular use deep cycling.

Which in turn is different from maintaining a Starter battery.

How do I do a capacity test on my batterys,

Solar Panels connected to my house batterys run both my battery banks, very successfully,
RV has 380 watts of solar power, Unshaded, 400 amphrs
Boat has 500 watts of solar power, Unshaded, 200 amphrs

I bought this battery charger as a just in case,

But mainly for my new coiled AGM Battery that I use for a starter motor in my RV and my Boat, 75 amhr 900 CCA
It flicks the V8 diesel over instantly,

300 HP Turbo V8 Cat motor needs a bit of grunt and a full 12 volts to start it,
My RV house batterys wont even look at it, 400 amhrs supplied by two batterys,
The 27 HP Westerbeke in my boat flicks over with a few turns and fires up,
The 200 amphr AGM only clicks the starter motor on my boat,

With out a full 12 volts, The fuel solenoid on the cat motor wont open and supply fuel to the diesel,

So far Ive only tried it on dead batterys to try it out, To make sure its not a Dud before I use it on my house batterys,
If I ever do use it on my house batterys, I bought it purely as a back up if any thing does fail,
I also have the Pure Sine 3.5 KVA Generator with an inbuilt battery charger,
So thats another back up just in case,

[john61ct]

Originally Posted by Mr B

How do I do a capacity test on my batterys

Rough version, put on a 0.05C load, see how many hours from 100% Full down to 10.5V, then immediately recharge. Should be 15+ hours, or recycle.

More precisely - search for

20 hour capacity test here https://marinehowto.com/programming-a-battery-monitor/ Better yet read it all, *and check out the rest of the site.



Those House banks, when Full should have no issue cranking your engines, something wrong there for sure if they aren't at well over 12V.




I also have the Pure Sine 3.5 KVA Generator with an inbuilt battery charger

How many amps?

> Solar Panels connected to my house batterys run both my battery banks, very successfully

By what measure, how do you know, objectively?


> RV has 380 watts of solar power, Unshaded, 400 amphrs


> Boat has 500 watts of solar power, Unshaded, 200 amphrs

What are those Ah numbers measuring?

If you want more detailed help, best to layout all the details, links to the specific models involved etc, in your own new thread.