Why oh why

This past weekend we had our final family get-together of the year on our off grid property.  All went well with the lights working well in my  17 building western town.  For overnight use my Son-in-law uses a CPAP machine and the next morning I asked him if all went well with the machine.  (For this CPAP I was able to connect my 1000 watt inverter.)  He replied that it worked until about 4 AM when it shut off.  I really like my SIL so I don't want to kill him.
I checked the batteries with a hydrometer and found both end ones in  the 4 in series were at their normal 1.300 reading, which seemed strange after 4 or 5 hours of light bulb usage in many of the buildings PLUS 4 or 5 hours of CPAP usage, and equally strange was the two center batteries were at 1.250.  I did a full charge as the  sun rose then did 3 one hour equalizations which seemed to fix the glitch.  By the way the next night his CPAP worked perfectly all  night but I did connect his hotel room to my 2500 watt inverter in case the inverter was the problem.
All three inverters seem ( I failed to mention the 500 Watt one I also use for smaller loads ) to be working well

My simple question is why did the 1000 Watt one shut off ?  Im suspecting that lack of doing my equalization routine over the past few months caused this since doing 3 hours worth seemed to fix it.   Possible?