Actual lifetime of 18650 cells
Besides Battery voltage outside rated Vmax.~Vmin. range, the biggest ageing factor on LiPO4 is thermal stress. 

For example from datasheet specs below.


  Cycle life : 400 cyc, charge 1.5A, discharge 4A (80%)   ESR=80 mOhms {new}


Look at Power dissipation, Pd, when new. and maybe 2x to 3x when getting old and >10x when dead.
\$P_D=I^2\cdot ESR [\Omega]\$ = 4²*(0.08~0.24)Ω=225~675mW to 2.2W when dying under CC. If you can imagine the temp rise of a part this size dissipating this power, LG are very conservative on temp rise and ageing effects are a runaway condition where the weakest cell dies 1st.

It is difficult to compute your answer but you can try but notice DoD&lt; 50% makes the biggest effect. i.e. preventing Vbat &lt; ~3.4V (my est.)

Now review my charts of Batt.Univ. research.



REF  My chart uses data from Batt. University tables of research on new LiPO4 cells

If you want a rated lifetime capacity 600 cycles using 4.2V at some Ah rating is a compromise of total charge cycles and capacity for a new LiPo4 cell.   Some cells might be rated at higher lifespan or higher capacity and specs for CV and CC and C rates used in the specs must be compared to get meaningful results.

If you wanted max lifetime charge Ah*N cycles you keep the cells at mid- charge levels (SoC= 60%) and every 10 to 15 cycles charge to 4.2 to replenish the soaking capacity then resume to mid-charge voltages. Then using only 20% DoD from the initial charge capacity or SoC = 60% to 40% using Coulomb counting calibration methods you might achieve 14k cycles/600 *90% duty cycle rated = 21x the lifetime capacity. 

If you used a CV of 3.9V vs 4.2V you gain 3200 cycle/900rated=3.5x rated cycles but lose 35%= 100%-65% capacity unless you periodically use 4.2V every 10~15 cycles which restored some "memory capacitance". otherwise the net gain is 3.5x 65% approx. doubles the life capacity.

You cannot combine the  20% DoD at mid charge with periodic 100% charges @ 4.2V every 10 cycles and use 3.9V CV because the life span from self-discharge chemistry away from mid-charge is not charted but is known to reduce life span. 

You cannot expect 3.5 x 2= 7x 900 cycles of some Ah*Vavg/3600 cell Joule energy discharge but 350% x 600 cycles is certainly worth considering.  

This means you might need 5x as many batteries using only 20% of the rated capacity. Also charging them 5x more frequently is a PITA, unless you have some convenient way with backup storage and a transfer switch but then they all last 21x longer. 

Although these LG cells may have a minium rating of 3400mA this independent test showed less capacity than rated.


Official specifications:
Nominal Capacity: 3500mAh
Minimum Capacity: 3400mAh
Nominal voltage: 3.635V
Standard charge: 0.5C (1700mA) 4.2V, cut-off 50mA
Max. charge voltage: 4.2V +/- 0.05V
Max. charge current: 1C (3400mA)
Standard discharge: 0.2C (680mA), cut-off 2.5V
Max. discharge current: 10A
Weight: Max. 49.0g
Cycle life : 400 cycles, charge 1.5A, discharge 4A (80%)
Operating temperature: Charge: 0° ~ 45°C, Discharge: -20°C ~ 60°C
Storage temperature: 1 month: -20°C ~ 60°C, 3 months: -20°C ~ 45°C, 1 year: -20°C ~ 20°C