AGM Battery Over-discharge Damage?

[Horigan]

I have a Marine dual use 12V AGM battery that I over-discharged to 8.5V. It's charging back up now. I understand over-discharging a battery can damage it, or reduce it's capacity. After charging it I'll take it to an auto parts store for a load test. If it passes that load test are there any concerns remaining with the battery?

 

[eric102]

If you didn't let it sit discharged for any length of time and are using a smart AGM battery charger it might be OK.

If it has been discharged for a while and you are using a standard flooded cell battery charger it will probably be toast or if you are lucky usable but at a reduced capacity.

 

[Horigan]

Thanks. I have smart AGM charger and it charged up fully and tested good at the auto parts store with their load tool. It wasn't discharged for very long, a day or two. Looks like I was lucky. I

wish I knew more about how the auto parts battery testers work relative to amp-hour capacity. I get how it checks for cranking amps, but not sure how well it checks for overall amp-hour capacity, which is my concern when doing over-nighters.

 

[eric102]

I've been using a SOLAR BA9 battery tester for a few years and its a great way to keep track of a battery's condition, much better than a simple pile load test. It will show CCA available, percent of charge, battery health and more.

https://www.amazon.com/BA9-40-1200-...ttery+tester+solar&qid=1571339704&sr=8-7&th=1