Docking station tech is lame at best. First the battery charging logic
is flawed. The charger should disconnect from the battery once it is charged.
It should test the battery once an hour thereafter and decide what to do. I cannot
tell you how many batteries I have had die from long term over charging and
lack of correct dynamics in use.
A docking station should have cooling designed to keep the battery as well
as the CPU/logic cool. Most obstruct air flow and do neither well.
This depends entirely on the laptop/battery. The last two Lenovos I've had both offered smart charging where the battery would optionally not begin charging until below X% and would stop when the battery signaled it was full. The charging threshold could either be directly specified by the user or determined by the laptop based on usage pattern.
My previous machine I set to not recharge until below 85%. It was a power hog so the battery was pretty much a pack-along UPS. 15% represented a fairly small number of minutes of operation.
My current Thinkpad is vastly better on battery. I can get well in excess of 4 hours of casual use from a single charge. I quite often use it unplugged so I have the threshold set higher since I'm more likely to need that extra capacity.