I'm not an expert on this, but did some research on the modern cell phone and tablet batteries. It used to be that to keep your batteries "well conditioned" you should run them down and then charge up and not charge so much in-between.
But with modern batteries that is no longer necessary. The battery capacity depends on how many full "charging cycles" it has gone through. But a "cycle" is not a "single charging period." It depends on what percent battery is charged.
If your battery level is at 50% and you charge it to 100%, and then the next day it goes to 50% again and you again charge it to 100% that is one full cycle (50% + 50% = 100%, just once).
The battery should be ok and hold a decent charge for at least 500 battery cycles. Micro-charging therefore should be ok. If you top off your charge when it's 90% full and do that 10 days in a row that is still the equivalent of one full cycle.
And the charging should cease when fully charged.
So basically it seems the best thing to do is just charge it when it's convenient and not really worry about it.
doug