Testing AGM Batteries?

[jackhartjr]

Hi folks, what equipment would best be used to test AGM batteries?
The guy at Deka Battery said I needed a $700.00 Carbon Pile machine! Surely it can be done for less than that!
Thanks in advance!
Jack

 

[Maine Sail]

Are you testing them for Ah capacity or starting ability..?

 

[jackhartjr]

I am testing them to be sure they are still good. I have 10 group 31 AGM's in my truck that in addition to starting the truck, run a 10,000 BTU Dometic APU, (Auxiliary Power Unit)! (It shuts off when the bank gets down to 10.5 Volts. Charges during the day via a 320 amp, 3 stage alternator!) To keep it sailing related, I will have the same battery in the sailboat!

 

[Maine Sail]

10.5V is murder on those batteries. For optimal longevity they really should not dip below 11.7V under high loads and 12.2V for light loads.. The best test is to run a 20 hour test at 75-77F. Apply a fixed load of Ah capacity divided by 20 (5A for a 100Ah battery or 6.25A for a 125Ah battery)and start a count down clock. When the battery hits 10.5V check how many hours and minutes it ran. This is your % of usable capacity left. It is best to keep the discharge load constant as the voltage decays and light bulbs or resistors can be used for this or even a PWM dimmer..

 

[Benny17441]

You can find a cheap carbon pyle load and battery tester for under $75 at Northern Tools. It may not be a professional tool but it could quickly point out a faulty battery or one with a largely diminished storage capacity. If reliable measurable results about storage capacity are required I would then defer to the 20 hour test as indicated by Maine Sail. For a simple practical test just to determine if the batteries are "good enough" to take the truck on the road I would, after testing them individually with the battery tester, to test the combined bank under actual usage conditions. Charge them fully, run the A/C for 10 hours and then crank the engine. If it performs adequately I would feel fairly comfortable about taking it on the road. I concur that the same concerns would apply for a marine installation. The problem in a sail boat is that we would not have the recharging capacity of a 320A running for hours.

 

[jackhartjr]

Maine Sail, that APU system was designed for doing this day in and day out, most folks have 7 batteries in order to get about 7 to 8 hours a night air conditioning, I added three more to my system to get roughly 10 hours a night! It works rather well, when you have the right inverter! I had one that wasn't pure sine wave, I am getting ready to get a Xantrex 2.0 that should make it more efficient! One of the fleets in my area have been using the Dometic APU's for several years, they run several hundred trucks with very few problem!
It also has a shore power plug that will fully charge the batteries when I'm home on the weekends! The shore power will also run the unit! Several truck stops and more and more rest areas are equipped with electricity to make that easier!