I came across some interesting articles and research on the website below, covering a wide range of topics from battery use in EVs, to battery charging, temperature and depth of discharge usage characteristics:http://batteryuniversity.com/learn/arti ... vehicle_evhttp://batteryuniversity.com/learn/arti ... _batteries
It is interesting to realize in Table 4 on the 2nd page referenced there, that with an 8 year "design" for EV battery life, that would lead to almost 3,000 charge/discharge cycles on the battery. To achieve that, it looks like the maximum cell voltage is reduced to achieve better longevity. With 192 batteries in our battery pack, they must be wired in a combination of series and parallel formats, to the equivalent of a series string of 96 sets of 2 parallel batteries, and a cell charging voltage of approx 3.95 VDC @ 84% charge (based on what I have noted as a charging voltage at a DCQC station of approx 390 VDC) ... which would indicate the batteries are only used to approx 60% (or less) of their fully usable capacity in order to achieve the approx 3000 charging cycles.
There is also lots of info on that website on cell phone battery tests and longevity ... all interesting reads for those who want to understand the batteries in our vehicles.
Indeed the second article has some nice tables/figures: http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
Figure 1: Capacity drop as part of cycling.
Table 2: Cycle life as a function of
depth of discharge. A partial discharge reduces stress and prolongs battery life, so does a partial charge. Elevated temperature and high currents also affect cycle life. Note: 100% DoD is a full cycle; 10% is very brief. Cycling in mid-state-of-charge would have best longevity.
Table 3: Estimated recoverable capacity when storing Li-ion for one year at various temperatures. Elevated temperature hastens permanent capacity loss. Not all Li-ion systems behave the same.
Table 4: Discharge cycles and capacity as a function of charge voltage limit. Every 0.10V drop below 4.20V/cell doubles the cycle but holds less capacity. Raising the voltage above 4.20V/cell would shorten the life. Guideline: Every 70mV drop in charge voltage lowers the usable capacity by about 10%. Note: Partial charging negates the benefit of Li-ion in terms of high specific energy.
Figure 5: Effects on cycle life at elevated charge voltages. Higher charge voltages boost capacity but lowers cycle life and compromises safety.
Figure 6: Capacity loss when operating Li-ion within given charge and discharge bandwidths.
Batteries charging to 85% have a longer life span than enabling full charge. Although longer lasting, a less than full cycle does not fully utilize a battery.
• 75–65% SoC offers longest cycle life
• EVs use 85–25% SoC to prolong battery life
• 100–25% SoC gives long runtime, makes best use of battery, but reduces battery life.