Recently I installed a solar panel. I used a 12 volts Sealed Lead Acid Maintenance Free battery with it. There was a huge lot of confusion as to what to set the minimum voltage or cutoff voltage. The charge controller came with a preset of 10.8 volts. But on the internet many forums and sites suggested to keep the cutoff voltage to around 11.5, some said I can go as low as 9.0.

Confused I started going through manuals or leaflets of battery companies and understood that it better to refer to the manual or leaflet or company information than to rely on the random articles and forum posts on the internet.

The minimum voltage or cutoff voltage to be set is actually not simple and straight. It varies with the amount of current drawn over the required time period and environmental temperature should be considered also.

My battery manufacturer (Amaron) says that at a temperature of 27 degree celsius and a current drawn of about 0.6 amps the battery can be discharged down to min of 1.75 volts per cell – that is a total of 10.5 volts for the 12 volts battery.

As per SLA battery datasheets, the general relation is the more the current drawn the less can be the minimum discharge voltage and the less the current drawn the higher will be the cutoff voltage. This is because when a higher current is drawn the voltage drop will be more and at a certain point the voltage drop will reach the cutoff voltage or the current flow will fall a lot due to the high voltage drop and the load should stop working. Batteries can recover a bit from this type of deep discharge as some chemical will still be left for the reaction to happen. But with smaller current drawn the voltage drop will be less or the current drawn is more linear over the required time period, hence in cases of lower current drawn a voltage drop to minimums will be more or less actual and the battery has lesser or no chance of recovering from such deep discharge after disconnecting the load.[1]
Added to this, higher the temperature, the lower the available capacity.

But remember the more the battery is discharged (percentage of capacity) the lesser will be its life. So while setting the cutoff voltage weigh the battery life vs the need for deep discharge.

All said, please do refer to your battery manual or company information brochure for the proper voltages and ideal discharge rate.

[1] Please note – you can test the current drawn vs remaining capacity  practically this way – connect a load that draws high current, set the cutoff voltage to a safe limit (10.8 would be good for a 12v sla single unit). After the voltage drops to 10.8 volts and the load disconnects, wait for some time. The voltage will soon go well above 10.8 volts (should be near or around 12 volts). Then connect a load that will draw only a few milli-amps and see that the voltage will drop slowly over a longer period of time. Now connect the higher current load again and you will see the voltage will drop instantly to 10.8 or lower.

References:
https://www.power-sonic.com/wp-content/uploads/2018/12/Technical-Manual.pdf
https://www.quanta.in/old/images/pdf/Quantamanual-new.pdf
https://www.quanta.in/old/images/pdf/Quanta%20Life%20Line%20Booklet.pdf
https://www.quanta.in/old/images/pdf/Quanta%20Silver%20Book.pdf