11.5 is seriously low for a 12 V battery: for a flooded lead acid battery at rest, 12.6+ is full and 12.2 volts is a 50% state of discharge. (AGM batteries tend to run 0.1 - 0.2 V higher) You really don't want to run them below 50% state of charge if you can avoid it. The deeper you cycle them, the more it shortens their life. 17 volts is high enough to damage the battery.