The rule of thumb is you roughly double cycle life for every 0.1v lower you go (approx. 10% of charge). I would only restrict the full charge level of you neve

The rule of thumb is you roughly double cycle life for every 0.1v lower you go (approx. 10% of charge). I would only restrict the full charge level of you never need the full charge available anyway. Eg. I only use about 60% of my phone's battery, so I can comfortably restrict it to 85% and have plenty of leeway to avoid running out. If there's a decent chance you need the full battery, just use the full battery. Also consider how long you expect to keep a device. A couple of years of daily charging is 700 cycles, so worth considering preserving battery lifetime if it suits you.