Lithium batteries have short lifespans unless you're only using a fraction of their capacity, high environmental toxicity, and are extremely expensive.
In regards to lifespan to cycling, you are thinking of lead acid batteries, lithium batteries can be deep cycled all the time. When your phone gets to a few percent battery life, it is being deep cycled pretty heavily.
There does need to be some kind of undervoltage protection, because if drained under 3v batteries can be damaged, however by that point well over 99% of all the energy the battery has has been expended. I'd hardly call that "light cycling".
Modern quality lithiums can be deep cycled somewhere between 500-1000 times depending. A 2-3 year life full cycling once a day isn't too shabby at all.