johnlocke said:
According to Jeff Dahn, a cycle is a cycle. Partial cycles add up to full cycles. Three 33% to 66% cycles add up to one cycle. The leaf battery is never charged to ultimate capacity (4.3 vdc per cell) anyway. Charging is stopped at 4.11 vdc per cell intentionally. A standard full discharge cycle is 4.3 vdc to 3.0 vdc. In the Leaf the discharge cycle is limited to 4.11 vdc to 3.2 vdc by design. Below 3.3 vdc, there is little power left in the battery and the discharge voltage curve falls off rapidly. Most people never come close to full discharge anyway.
A standard li-ion battery might be expected to last 300-400 cycles at a full discharge cycle. Turns out that for every 70 mv you lower the upper limit, battery life doubles. At 4.11 vdc as the upper limit, you could expect about 1500 cycles before the battery degrades too far to be useful. Leafs actually get that in cool climates. Nissan didn't account for degradation at higher temps though. The lack of a TMS in the leaf battery pack was a cost cutting measure that causes Leafs to significantly degrade in hot weather.
Lowering the upper limit to 4.0 vdc does improve battery longevity somewhat but the effect of lowering the upper limit still further is marginal.
The reason that lowering the upper voltage works to improve battery life is that the anode swells significantly as the battery approaches full capacity which causes mechanical stress.
The above is different from "Tests are typically made using full charge and discharge cycles, but my reading of this data is that every time you plug in to charge counts as a cycle." I don't agree that you just add fractions of cycles, regardless of their 'depth', but I'll admit that it
may be right. I don't see anyone agreeing with you that any charge, no matter how short or shallow, counts as a cycle.