testing AGM battery???

[clawman]

Is it possible to test an AGM battery to determine its health? Mine seems to be losing voltage faster than it did in the past.

[cyber16]

The best way to test ANY deep cycle battery is a longer controlled capacity test.
Place a known load onto the battery, lets say the battery is a 100Ah
Place a 5amp load for ten hours or a 10 amp load for five hours
After that, a 100Ah battery should be at 50% DOD
Now find one of the many state of battery charge charts online, it's best to use one that has temperature compensation.

If the rested voltage reads under 50% then you have reduced capacity which is normal wear depending on age and discharge history.

If it reads near 50% DOD then maybe the load you are placing on it is greater then you think, you can test that as well with a dc amp clamp meter.

If it's suppling a trolling motor, maybe wind/current & drag, OR the motor is drawing more current due to worn brushes or a little water intrusion.

Since I am kind of into power inverters, I would just take the battery and hook it up to one of my higher end units and use the dc shunt ammeter with a known load.

AGM or standard flooded deliver AMPs based upon hours, an amp is an amp

[REW]

Purchase and use a battery load tester to determine the health of any storage battery of 12 volts.

https://www.northerntool.com/shop/to...7843_200797843

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Or just bring your battery or boat by a "Batteries plus" battery store and they will test your battery for you.

Many auto stores or other retail outlets also have the appropriate battery tester to perform an excellent battery test on your aqm battery.

Best wishes.

[cyber16]

Those load testers are not a good test for deep cycle capacity.
I have a couple higher end carbon pile testers, they basically test the capability of delivering high energy from the battery under a short cycle.
While most of todays AGM batteries use thin plates which can delivery vast amounts of energy for engine starting purposes, unlike some flooded deep cycle types that use thick plates for longevity of mid current draws.

Delivery of a short high amp draw won't give you a current ah capacity number when done

When clawman said losing voltage faster than it did in the past. I assumed he was speaking more of the deep cycle performances of the battery

[REW]

Cyber,
Copy that - you are 100% correct.

As an earlier post suggested - put a moderate load on the fully charged battery and measure the time until the voltage goes down on the battery.

If you wish, a very convenient load is a High Sealed Beam head light bulb.

These bulbs will draw between 10-15 amps and you can be discharging the battery - while you are doing something else nearby - If you happen to be doing the test at night, you can keep an eye on the headlight and make note of the time when the light has dimmed to a pretty low brightness level.

Then, compare the discharge time using the same headlight on a brand new battery and you compare your battery to a new one.

To ease the job, just pick up a sealed beam headlight from an auto parts store and also pick up a headlight socket for the light at the store or from a junk yard out of a wrecked car.

If you want to save money you can get both the light bulb and the socket from a junked car at an auto parts junk yard for a couple of $$.



Best wishes.

[Ltrain]

Great info in this thread, thanks guys

[CI_Guy]

The digital testers at Batteries Plus and auto parts stores has a setting for testing deep cycle batteries. Most of the people working there only test auto batteries but if you ask them to test in the deep cycle mode they can.