The quick answer is NO HARM...
It does seem however to drop down rather fast for that short of time.
My two 12VDC GP24 Interstate vatteries have been sitting outside in the battery box totally dosconnected since late October last year and I just checked them a couple weeks back and they read 12.6VDC. They were on the converter/charger about two months back for three or four days.
consider this chart showing DC Voltage verses state of charge of deep cycle batteries...
You should not ever let a deep cycle battery discharge below the 0% SOC or 10.5VDC or it may do damage to the battery.
Most of us like to not let the deep cycle batteries drop below 50% SOC or 12.0VDC.
Roy Ken
My Posts are IMHO based on my experiences - Words in CAPS does not mean I am shouting
Roy - Carolyn
RETIRED DOAF/DON/DOD/CONTR RADIO TECH (42yrs)
K9PHT (Since 1957) 146.52M
2010 F150, 5.4,3:73 Gears,SCab
2008 Starcraft 14RT EU2000i GEN
2005 Flagstaff 8528RESS