Be careful, Dan. True deep-cycle batteries, like golf-cart batteries and fork-lift batteries, are reasonably resistant to problems from deep discharge. But RV / Marine batteries, including the Interstate batteries supplied with the TM, are NOT true deep-cycle batteries. They handle deep discharge a bit better than standard car batteries - but not much. It is wise to limit depth of discharge to around 50%.
Several reputable sources for lead-acid battery info (not manufacturer's claims) agree on this. One is
http://www.uuhome.de/william.darden/...tm#differences
At this site, you read the following:
"Car batteries are specially designed with thinner (.04 inch or 1.02 mm) and more porous plates for a greater surface area to order produce the high amps required to start an engine. They are engineered for up to 5,000 shallow (to 3%) discharges, which is over four engine starts per day. Starting batteries should NOT be discharged below 90% State-of-Charge. They use sponge lead and expanded metal grids rather than solid lead. Marine starting batteries are a comprise between a car and deep cycle battery and are designed for starting and prolonged discharges at lower amperage that typically consumes between 20% and 50% of the battery's capacity. Motive and stationary deep cycle batteries have much thicker (up to .25 inch or 6.35 mm) plates, more lead, and weight more than car batteries the same size. They are normally discharged between 20% and 80% at lower amperage."
Bill