Trojan's can go down a lot deeper than that.
Per the trojan battery user guide:
- Do not discharge your battery more than 80%. This safety factor will eliminate the chance of overdischarging and damaging your battery.
that means you should be ok going down to 100-80=20%.....
20% state of charge is 5.83 V on a 6 volt battery or 11.66V on a 12 volt battery, according to their user's guide
http://www.trojanbattery.com/pdf/Tro...UsersGuide.pdf