Cheap Reliable Battery Load Testing
https://www.harborfreight.com/500-amp-carbon-pile-load-tester-91129.html Bulletproof way to test wet and AGM batteries Like a hospital heart stress test EDIT: Fixed the URL.
Forum Discussion
I have an AGM 8D 250AH battery that I had to take out of the RV because it would run perfectly for a while doing low amp RV work (furnace etc) but then would collapse under higher amp inverter loads.
Apparently I must have damaged that battery doing high amp tests to find out whether my new inverter's low voltage alarm worked properly. The inverter worked properly, but after that, the AGM started to act up. Based on my reports here on just how it acted, Mex thought maybe it had warped plates.
I could not tell anything was wrong with that battery until it started to collapse one time while camping. I did a capacity check by running a load at its 20 hr rate for 10 hours to try for 50% SOC, and it only did 6 hours and voltage indicated it was at 50% SOC already.
So what I had was a damaged battery that would no doubt fail the "load test" like in this thread, but it was still a usable 150AH battery for low amp loads (60% of 250). So I still have it, but not in the RV.
This may be an odd case where the capacity loss is not from sulphation, but is from damage.
It now sits in the stick-house garage as part of a UPS set-up to keep the internet going if we have a power failure like when a tree falls on line in a storm. Had a power failure like that a few weeks ago that lasted for several hours till Hydro got it fixed, and the UPS worked great. So that broken AGM is still useful for something!
So I do think there is a difference between a broken battery that can be revealed by a "load test" and a good battery that just does not have much capacity anymore. The load test might well show that the good battery has lower capacity than it ought to have, but perhaps not show just how much usable it still has. That is what the capacity test does. But you must decide when the capacity remaining is not enough anymore for the job it was doing.
OTOH, if it also has low resting voltage or shows a bad cell by hydrometer, that would mean it is totally broken and you can't use it anymore.
Apparently I must have damaged that battery doing high amp tests to find out whether my new inverter's low voltage alarm worked properly. The inverter worked properly, but after that, the AGM started to act up. Based on my reports here on just how it acted, Mex thought maybe it had warped plates.
I could not tell anything was wrong with that battery until it started to collapse one time while camping. I did a capacity check by running a load at its 20 hr rate for 10 hours to try for 50% SOC, and it only did 6 hours and voltage indicated it was at 50% SOC already.
So what I had was a damaged battery that would no doubt fail the "load test" like in this thread, but it was still a usable 150AH battery for low amp loads (60% of 250). So I still have it, but not in the RV.
This may be an odd case where the capacity loss is not from sulphation, but is from damage.
It now sits in the stick-house garage as part of a UPS set-up to keep the internet going if we have a power failure like when a tree falls on line in a storm. Had a power failure like that a few weeks ago that lasted for several hours till Hydro got it fixed, and the UPS worked great. So that broken AGM is still useful for something!
So I do think there is a difference between a broken battery that can be revealed by a "load test" and a good battery that just does not have much capacity anymore. The load test might well show that the good battery has lower capacity than it ought to have, but perhaps not show just how much usable it still has. That is what the capacity test does. But you must decide when the capacity remaining is not enough anymore for the job it was doing.
OTOH, if it also has low resting voltage or shows a bad cell by hydrometer, that would mean it is totally broken and you can't use it anymore.
