Problem with AGM 100AH, 12v, Voltage dropping from 12.9V to 12.5V under load.

[Runningslipper]

FIrstly,
Hi eveyrone !
I bought my 100AH battery (connected to solar charger and panels of course) 2 months ago.
I only discharged it to 50% once and then didnt use it much apart from occassional 10AH per day
When I first 50% discharged it was my 50W fan, It run for about 7-8 hours fine. The voltage was 12.24V when i turned it off.
It was roughlt 2 months ago.
Now when im connecting my 50W fan in the evening the voltage under load is showing 12.5V !! Dropping from 12.9V to 12.5V when i turn my fan ON.
After 2 hours the voltage is showing 12.1V (under load). WHen I turn the fan off the batt.is showing 12.6V tho.
When I tried to connect my PC (13A) my inverter just switched off showing not enough of voltage which is unusual coz even my 12v 9ah UPS batt can run my pc for apprx 5mins.
What happened ? How can i fix it ?

[SunEagle]

FIrstly,
Hi eveyrone !
I bought my 100AH battery (connected to solar charger and panels of course) 2 months ago.
I only discharged it to 50% once and then didnt use it much apart from occassional 10AH per day
When I first 50% discharged it was my 50W fan, It run for about 7-8 hours fine. The voltage was 12.24V when i turned it off.
It was roughlt 2 months ago.
Now when im connecting my 50W fan in the evening the voltage under load is showing 12.5V !! Dropping from 12.9V to 12.5V when i turn my fan ON.
After 2 hours the voltage is showing 12.1V (under load). WHen I turn the fan off the batt.is showing 12.6V tho.
When I tried to connect my PC (13A) my inverter just switched off showing not enough of voltage which is unusual coz even my 12v 9ah UPS batt can run my pc for apprx 5mins.
What happened ? How can i fix it ?

Chances are that AGM battery has been used up when you went to 50% and will no longer show enough voltage.

[Runningslipper]

LOL isnt 50% discharge what keeps those kind of batteries for years...not 1 time instance ?
50% discharge is recommended for agms...

[solardreamer]

You can't leave a LA/AGM battery discharged that far below floating voltage for 2 months. It's likely permanently sulfated.

[Runningslipper]

You can't leave a LA/AGM battery discharged that far below floating voltage for 2 months. It's likely permanently sulfated.

I didnt. It always in trickle charge mode when not used. Its connected to a solar charger. Forgot to mention its MPPPT tho. Its called "float mode" there.

[SunEagle]

I didnt. It always in trickle charge mode when not used. Its connected to a solar charger. Forgot to mention its MPPPT tho. Its called "float mode" there.

Well if the problem isn't the battery then you have another equipment problem.

I believe in the KISS principle which in my book means the battery can no longer provide a solid power source. Why it can't do this maybe because it was discharged too deeply or because it was not been properly charged so it didn't sulfate.

You can't think it is ok if you are now experiencing these issues.

[SunEagle]

LOL isnt 50% discharge what keeps those kind of batteries for years...not 1 time instance ?
50% discharge is recommended for agms...

Does the battery manufacture state that discharging to 50% is ok or does it state that the number of cycles is greatly reduced?

[Runningslipper]

Ive done some research and came across a similar problem on YT, problem with internal resistance it seems. https://www.youtube.com/watch?v=vsiaaBV3n7k
(however mine is not dropping THAT low!) -the first batt. problem in the video.
Apparently it has nothing to do with sulfication. Some ppl say it has smth to do with water being run out.
Since i dont thinki i will be able to open it i think it will stay like that forever im afraid.

[SunEagle]

Ive done some research and came across a similar problem on YT, problem with internal resistance it seems. https://www.youtube.com/watch?v=vsiaaBV3n7k
(however mine is not dropping THAT low!) -the first batt. problem in the video.
Apparently it has nothing to do with sulfication. Some ppl say it has smth to do with water being run out.
Since i dont thinki i will be able to open it i think it will stay like that forever im afraid.

AGM's are a little tricky since you can check the water level or the acid content. So measuring the voltage is the only way and that way can be very misleading of the battery condition.