Cycle depth? Apologies - 25 hour old Tesla owner
Depth of discharge - the amount of energy removed and then added to a battery compared to its capacity. 100% to 0% and back again is one cycle, but is also a 100% depth of discharge. 75% to 25% and back again twice is also one cycle, but with a 50% depth of discharge. 50% to 40% and back again 10 times is one cycle but with a 10% depth of discharge. But the total number of cycles (i.e. the amount of useful energy you can get out of the battery) before it degrades to a certain point is
inversely proportional to the depth of discharge (see Table 2), roughly tripling every time the average depth of discharge is cut in half, as well as inversely proportional to the upper voltage you were using when you were cycling the battery (see Table 4 in the previous link), where every 10-15% reduction also doubles the number of useful cycles you get. Calendar aging (aging associated with the battery simply existing over a certain amount of time, even if it is not used at all) is
inversely proportional to the state of charge at which the battery is kept. High temperatures are bad for batteries in storage, but are beneficial when fast charging because they make it where the ions can more easily move around.
Put it all together and for maximum battery life, you want to:
1. Charge as often as possible (minimize average depth of discharge)
2. Put as little charge into the battery as you can get away with (minimize upper voltage)
3. Charge the battery as close to your departure time as possible and drive the car immediately after you charge it (minimize calendar aging)