How many cycles depends on the application.  I use batteries for off grid solar systems.  I design for 50% DOD max.  There always exceptions as you might expect.  Even 6000 cycles is 16 years.  I just got 7 years on AGM systems I put in service in2010 and am changing out now.  Those were supposed to go 4 to 5 years.  I got the extra years by switching to grid at night and remove the load at night as long as the grid was up.  I am waiting to buy some Lithium batteries when they become available for retain customers.  Looks like right now Electtrovaya is only selling to OEMs.  My few systems do not qualify.