I have a 12 V, 55 Ah lead acid deep cycle battery that I am using to power a small cooler/fridge that will hold medicine for a community project that I'm working on. The goal is to provide continuous power to the fridge despite any power outages caused by natural disasters, and there will eventually be a solar system connected to lessen the load on the battery and increase the uptime. The full system will also have a switching module that will automatically detect when the grid (wall outlet) stops working and will switch to this battery (it will also do this in the other direction), like a UPS but much cheaper due to budget constraints.
Now, I am going to do an experiment where I run the 12 V, ~48 Wh cooler directly from the battery and log the voltage vs. time across the terminals so that I can tell how long the battery can power the cooler before it turns off and compare that to the expected result.
I have found plenty of tables from google that showing the depth of discharge percentage vs. battery voltage, and it says it shouldn't drop below 12 V until the battery is about 60% depleted. This is desirable because I do NOT want to completely deplete the battery and reduce its lifespan.
Here is what I am unsure of, the fridge operating manual does not provide any information about the lowest operating voltage. Can I assume that the lowest operating voltage is close to 12 V, and that the fridge will shut off once the battery reaches, say, 11.5 V? If yes, then I am good to go. If not, then what is an average operating voltage range for a system that is designed for 12 V?
(I know that it is likely very dependent on the system, but I am looking for more of an anecdotal answer. If an answer is not obvious, then I can attempt to use a variable power supply in the lab to find out the voltage at which the fridge stops drawing current, though I am asking here because I'm in a bit of a time crunch to assemble the first prototype and would like to be able to run this experiment as soon as possible)
Edit: for reference, here is the only information I could find about the cooler https://secure.img1-fg.wfcdn.com/docresources/0/156/1564815.pdf