Fully charged battery depletes at night with no loads attached

[UnderTheSun]

Problem: Our 12V/200Ah AGM battery goes from 100% capacity in the daytime to depleting to about 75/85% at night with no AC or DC loads attached. The usual operation has solely been the charge controller being on and charging/maintaining the battery throughout. No loads are attached.

Array description and application: A 12 volt system, small array to solely power a low-voltage landscape lighting transformer. The maximum wattage the transformer draws is 50 watts. However and again, we’re currently not using the transformer (AC load) nor any DC/12V loads.

Attempted pinpoint: We ran a test by turning off the both PV-In breaker and charge controller breaker before end of day at dusk to maintain the battery’s 100 percent level. There was a check around 2.00a and the battery was at 95%. At dawn, the level was at 94%. This was done for the past two nights with the battery only losing a small percentage of charge. However, when the charge controller is turned on and let’s say by 2.00a that evening at checking, the battery level has dropped.

So in essence, it is a daily routine/cycle of the charge controller topping off the battery during the day, then something uncertain depletes the battery at night, to the charge controller refilling the battery again the following day.

Any suggestions? Thank you!

Equipment:
1 x 200Ah Renogy AGM battery
1 x 30A Renogy Rover charge controller
1 x 12V/300W Sure Sine inverter
2 x 100W Renogy mono panels
1 x MidNite Solar SPD

 

[Mattb4]

Run a load test of battery.

 

[Zwy]

Problem: Our 12V/200Ah AGM battery goes from 100% capacity in the daytime to depleting to about 75/85% at night with no AC or DC loads attached. The usual operation has solely been the charge controller being on and charging/maintaining the battery throughout. No loads are attached.

Array description and application: A 12 volt system, small array to solely power a low-voltage landscape lighting transformer. The maximum wattage the transformer draws is 50 watts. However and again, we’re currently not using the transformer (AC load) nor any DC/12V loads.

Attempted pinpoint: We ran a test by turning off the both PV-In breaker and charge controller breaker before end of day at dusk to maintain the battery’s 100 percent level. There was a check around 2.00a and the battery was at 95%. At dawn, the level was at 94%. This was done for the past two nights with the battery only losing a small percentage of charge.

Are you using solely voltage to determine SOC? I assume you do not have a coulometer.

Open circuit voltage of a battery is no indication of capacity.

I would use a coulometer to run a capacity test from full charge and compare to the factory specs for the battery.

Most likely the battery is sulfated.

However, when the charge controller is turned on and let’s say by 2.00a that evening at checking, the battery level has dropped.

So in essence, it is a daily routine/cycle of the charge controller topping off the battery during the day, then something uncertain depletes the battery at night, to the charge controller refilling the battery again the following day.

If you had a coulometer you could see if indeed any current is flowing. It can also be done using a multimeter and the internal amps function. It is possible the charge controller is defective. Only way to know is to test.

Any suggestions? Thank you!

Equipment:
1 x 200Ah Renogy AGM battery
1 x 30A Renogy Rover charge controller
1 x 12V/300W Sure Sine inverter
2 x 100W Renogy mono panels
1 x MidNite Solar SPD