What chicken scratch I can tell you.
Yes, over discharging isn't healthy for the battery, IMHO I would call 30% the limit
before I turn off or disable features until I get to a charger.
However for new batteries I would, discharge to 20% "once" to heat up the battery & expand its endurance, I do recommend that.
Many devices now, record what you just stated, only in life terms instead of current usage
. For instance you can predict how long your battery is going to last.
9/10 a monitor will give you the active precentage with the current voltage of the battery, usually is supposed to start at 3.8-3.9 new.
If you ever reach 3.0v(in life term, not current), by this time, you can tell first hand that its not holding a charge as well as it should or its charging way too fast withing a short period. ITs time to replace it.
Of course you have some instances where the battery cannot be change by the user (i.e I have a Palm TX thats getting close to 3.0v)
Yeah it sucks to see its getting close & the only thing you can do is ship it to the OEM while you get charged a premium.