Charge up to 75 percent and ideally run down to 25 percent before charging up for normal weekly use.
Correct everyone??
No, running it down to 25% before plugging in is not ideal practice. That's a flawed conclusion from this one flawed data point.
Ideal is technically to keep your battery as close to 50% as possible, but you really shouldn't worry about it too much. Best to always make sure you have enough charge to handle unexpected trips.
Say you are sure you only need 10% capacity per day. Then it's better to plug in every day and keep it between 55% to 45% than to run it down from 75% to 25% over 5 days and plug in every 5 days.
Problems I see with the 75%-25% conclusions reached from that one graph:
1. Go to original IEEE paper that it was taken from and you'll see that the authors didn't reach that conclusion, or have those notes below the graph. This is just one example of a Dynamic Stress Test from a single manufacturer for a specific battery.
2. The graph is one manufacturer's results for a specific LMO battery. Tesla doesn't use the LMO chemistry in their batteries.
3. The 90,000 vs. 150,000 EU calculation is simply wrong. The 90,000 assumes that the 75-65% line crosses 90% at 9000 test cycles. The data doesn't go out that far. Maybe it crosses 90% at 15000 test cycles, which would give 150,000 EU. We don't know.
4. If you compare 75-65% to 75-25% at actual known points on the graph, you don't see much difference. Take the 95% retention point. 75-65% crosses at about 3000 test cycles, 75-25% crosses at about 600 test cycles. Both are then equal at about 300 EU.
5. The 75-65% has an average SoC of 70%, while 75-25% has an average SoC of 50%. A fairer comparison would be 55-45% vs. 75-25%.
6. This specific Dynamic Stress Test doesn't necessarily represent real world degradation over time. It also doesn't take into account any benefits of battery conditioning that you'd see by keeping your car plugged in more often.