mkjayakumar wrote:Given that Leaf has 24kWh (I was told in this forum), then wouldn't an 100% usable charge of 21 kWh is actually ony 87%, and an 80% charge (which is 16.8kWh) in reality only 70% ?
I believe that Phil managed to get exact SOC readings out of the battery ECU and determined
that full charge corresponded to 94 or 95%. 80% charge is what it says, and not less, as many of us have previously assumed.
In addition to what's been already said, please consider that the charge sustaining
mode on the Volt kicks in around 22 or 23% SOC. Presumably, you can drive the vehicle in this mode for months on end, and GM engineers thought that this SOC offered a good trade-off between range and battery longevity. I would not be concerned to let the Leaf sit at 20%, but if it was parked for an extended period of time (days and weeks), I would bring the SOC above 35% if possible.
The charts we are looking at are usually for generic LnMnO4 cells and they don't apply 100% to the Leaf. I would use them to get an idea of the characteristics and behavior of these cells, not an exact prediction of how the Leaf will behave. In addition to manganese dissolution in electrolyte Dave posted above, there are other processes that degrade the battery. I believe that at low SOC, Jahn-Teller effect will start impacting the spinel structure of the cell.
The owners manual (page EV-23) and these studies give us an idea of the speed of these processes as well. Dissolution into electrolyte, which seems to be dominant at high SOC, is typically measured in a matter of days. Spinel distortion due to Jahn-Teller effect is measured in a matter of weeks.
As a practical recommendation for a daily routine, I would try to keep the Leaf above the low battery warning (17% SOC). Dipping down to the very low battery warning (8% SOC) should be no problem, but you might not want to do it as part of your daily routine if possible (Luke is probably exempt from this). Turtle mode appears to be set fairly conservatively from a cell voltage perspective, but the SOC is so low that I would be concerned, and would not recommend doing that on a regular basis.
If you look at the annual battery report
that Phil posted earlier, Nissan keeps track of the number of turtle events and the number of hours spent at high SOC. It's pretty clear that they are doing this, because they think that it will impact battery performance. Note that they are lumping low SOC (0-20%) into one band and high SOC (>85%) into another (PKTIMEWHENHIGHSOCAFTERCHARGE, PKTIMEWHENHIGHSOCAFTERDRIVE, SOCATCG and TURTLELAMP).