Batteries not holding Voltage

[Garbonz]

Originally Posted by tkeithlu

I still occasionally use an old-fashioned load tester, but I've got one of these now, and it gives much more sophisticated information about battery condition. You punch in the type battery and its capacity, usually CCA, and it tels you the rest. It will also test your charging circuit, and that looks like it would be wise in your situation.

https://www.amazon.com/KONNWEI-100-2...TESTING_DEVICE

You need this, not that.

https://www.ebay.com/itm/180W-Consta...y/283956055277

You are looking for a deep cycle capacity test, not a LOAD test, which is for starter batteries.

[Garbonz]

Originally Posted by Cadence

Load test them. A static voltage test shows about nothing.

https://www.ebay.com/itm/180W-Consta...y/283956055277

[Garbonz]

AND, you should disconnect the individual batteries in your bank and run them through at least 2-3 charge/discharge cycles every year, and if they get below 80%, they are done.

There is NO OTHER way to do this for deep cycle batteries (cept Lithium). I have 10 year old Gel cell that are still at 80+ percent doing this one simple thing. The little device above is awesome, I used to have an adjustable load bank and a timer and have to set an alarm for 20 hours and check the load every hour or so. Now this thing does it all.

[Dieseldude]

If one battery is bad, it is not fully charging, and loading the others down. As a test, I would charge each battery individually, to as full a charge as possible. Then let it sit a few hours to stabilize. Then load test it. Repeat this for each battery, and you might find the bad boy.

[Amaranth]

I would like to thank you all for your many suggestions and assistance which is all of value.

By way of follow up I would like to provide;

Firstly for those who were concerned about getting the batteries fully charged or never fully charged. I do not believe this has been the issue as the solar array keeps them fully charged. I pretty much always return to the boat with the Batteries at 100% state of charge. Also when the bank was first put in we hooked up to shore power for some days to ensure the bank settled in correctly. Following this over the last 18 months of usage they have regular received a shore power "soaking"

We have now used a sophisticated battery tester on each individual battery and found wildly differing results. We then took out one of the batteries in the mid range of results and bench super charged this to see if it would respond. After a rest period the battery was in worse condition than before the charge.

So at this point we are heading the replacement journey in discussion with the suppler.

Again many thanks for all the assistance.