How to test AGM batteries?

How to test AGM batteries?

A guy here locally has some AGM batteries that are used (from a solar array) and is selling them cheap. He swears that they have been babied and never been discharged and always been on the best chargers available. I don?t have a lot of money to spend on this and I?d prefer not to have to get into lead acid batteries again so if I can get a couple of years out of these that would be great.

Is there any good way to test these things out?

Also, assuming they have been taken care of, how many years of life can one expect to get out of a decent AGM battery?

Thanks

Re: How to test AGM batteries?

An AGM battery is a lead-acid battery. You test an AGM battery just like you would test any other lead acid battery. You can measure its state of charge by measuring its voltage.

Most AGM batteries are good for a service life of three years. That is probably why the seller is selling them.

Re: How to test AGM batteries?

OK, so any decent battery tester should tell me if the thing is good right now. As to how long it will last, that's going to be a real gamble I assume.

Re: How to test AGM batteries?

Any battery from a solar array will have had many more cycles of discharge and charge on it than comparable trolling motor duty use (i.e. worn completely out!). Just buy a new one so your not disappointed, they are after all just a lead acid battery made in a unique way which offers some advantages compared to flat plate designs.

Re: How to test AGM batteries?

Found out more about them. Apparently they were used as backup power for a data center. So they were always trickle charged and apparently never drained. The solar thing was that these were topped off with solar, but only used if the mail power went out.

A new battery is great, but at the moment I need probably 6 for different things and I can get probably 5 or 6 of these for the price of a single new battery. So if I think I can get a couple of years out of them, its pretty compelling. ?If? is the key word here.

Re: How to test AGM batteries?

If they are that cheap, then go ahead and give them a try. The real test is a load test, but it's a specialized machine for that.

Volts will tell you that it is charged but how long will it hold that charge is the question.

Do you have problems in your area getting rid of them if they are doa? I think I have to pay to get rid of batteries here.

Re: How to test AGM batteries?

The only true way to test them is to put a constant load for a specified time then measure the volatge to determine what capacity they have. A load test for a short duration is not going to tell you anything with much accuracy. Basically, you are taking your chances buying these.

Re: How to test AGM batteries?

jhebert said:

An AGM battery is a lead-acid battery. You test an AGM battery just like you would test any other lead acid battery. You can measure its state of charge by measuring its voltage.

Most AGM batteries are good for a service life of three years. That is probably why the seller is selling them.

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Agree, 3 years is about time to start expecting problems, but there are a lot of variables involved and 3 is not an absolute I had one in a new '98 Dodge P/u that was still in it when I traded the truck in on an '07 (Dodge of course) but I never had one last that long before.......however I wouldn't purchase a 3 year old battery period.

Harbor Freight sells a load tester for a storage battery, including AGM's at about the price of a new battery. You have to test the terminal voltage under load and see how it holds up to really know the condition. Just measuring terminal voltage can tell you if you have a charge, but you need to know if it can deliver current from that charge.

If the lead-acid is sulfated up, it cannot supply 200 amperes of starting current and maintain anywhere near 12v. The meter has a green-yellow-red scale, and 200 amperes is a good number for starting current required on a host of engines. I really like mine and it has paid for it'self numerous times. Just crank up the current dial and watch the voltage.

Mark

Re: How to test AGM batteries?

My comment of an expectation of three years service for a typical AGM battery is based on my experience with 160 AGM batteries over the last six years. These batteries are connected in a series string of 40 jars, producing 540-Volts DC. The batteries are tested every few hours for their internal resistance. After three years we have found that about ten percent of the batteries will have their internal resistance begin to rise at a rate that is faster than the rest. Before four years has elapsed, we generally have replaced all batteries in order to keep the string reliable for its purpose, which is to furnish emergency power.

The batteries do not fail in three years, and, indeed, they are quite useful after three years. But in our service we have very low tolerance for failure, so we generally do not rely on them after four years.

If your application can tolerate using the battery until failure, you may be able to extend the useful service life of the battery longer than three or four years.

Battery life is very strongly influenced by environmental variables such as temperature, number of discharge cycles, precision of charging voltage, and depth of discharge. It is not unusual for a battery which is maintained on a constant and well-regulated float charge to last for 25 years or more, if it was designed for a long service life like that and for that application.

You can generally get an idea about the manufacturer's estimate of service life from the warranty that is offered. Cheap AGM batteries made in China and sold as a house brand at big outlet stores come with a one-year warranty for a reason.

Re: How to test AGM batteries?

Will, just as jhebert has discribed, we also have here on our site several hundred batteries (wet cells) which we have a maintenance program for. Monthly the specific gravity, float voltage, temperature, internal resistance and cleanleness is checked and recorded. About every 6 months they are put on an equalize charge. Failure is not an option.

These batteries will last many years if proper care is given to them. Ask them for the past inspection records for them if available and check to see how well they were maintained. You might have a great chance at some good batteries.

Durwood

Re: How to test AGM batteries?

jhebert said:

My comment of an expectation of three years service for a typical AGM battery is based on my experience with 160 AGM batteries over the last six years. These batteries are connected in a series string of 40 jars, producing 540-Volts DC. The batteries are tested every few hours for their internal resistance. After three years we have found that about ten percent of the batteries will have their internal resistance begin to rise at a rate that is faster than the rest. Before four years has elapsed, we generally have replaced all batteries in order to keep the string reliable for its purpose, which is to furnish emergency power.

The batteries do not fail in three years, and, indeed, they are quite useful after three years. But in our service we have very low tolerance for failure, so we generally do not rely on them after four years.

If your application can tolerate using the battery until failure, you may be able to extend the useful service life of the battery longer than three or four years.

Battery life is very strongly influenced by environmental variables such as temperature, number of discharge cycles, precision of charging voltage, and depth of discharge. It is not unusual for a battery which is maintained on a constant and well-regulated float charge to last for 25 years or more, if it was designed for a long service life like that and for that application.

You can generally get an idea about the manufacturer's estimate of service life from the warranty that is offered. Cheap AGM batteries made in China and sold as a house brand at big outlet stores come with a one-year warranty for a reason.

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Sir, I sincerely enjoyed reading your post and thank you for it.

Mark