I've known for some time that discharging a battery as little as possible will increase it's useful life .. however ..
The less you discharge .. the less time you get using your battery. That is ... if you stop at 70% you only get (pulling a number out of my hat) one hour before you need to stop. If you stop at 50% you will get much more time .. but the battery will not last as long before it needs to be replaced.
However we don't use our batteries every day. Likely not even every week. Yes, if you go for a week or two trip you will use it every day, but most of us just camp every once in a while on weekends.
So is the number of recharges (useful life) REALLY that much of a issue?
I'm getting a "battery monitor" that I can set an alarm to a specific voltage. http://www.batterystuff.com/battery-products/UPGvoltminder.html and will likely set it to around 50% for now.
ANOTHER THING ... I make it a practice of putting my battery on a charger once a week when I'm not camping. In the off season I will remove it, bring it inside, and put it on a float charger for the winter.