You'll still be lucky to get 300-500 cycles out of them if you go down to 20% charge or so. A 'Normal' car battery can fail in 30-150 cycles if you do that, hence the 'deep cycle' part of it.
Fine for a trolling motor, but if you're deep cycling them in a power system, that could kill them in a couple years. Usually you'll want to size them so you never go below 50% discharge on a normal basis.
