If it's not a good idea to leave a battery on a charger past the point where it's fully charged (either trickle or auto-sensor) then how come our alternators don't slowly kill our batteries when we're running our tractors (or cars, for that matter) all day.
Is there circuitry in the alternator that senses a full battery and stops feeding to it?
I don't know a thing about chargers and what's inside them, but I have a walk-behind self-propelled golf cart that uses a deep-discharge 12V battery and comes with a special charger that the manufacturer says to use not only to re-charge the battery after playing 18 holes, but that it's perfectly OK to keep the battery on the charger all winter long, not disconnecting it, nor using the battery at all....for months straight.
Maybe it's a unique kind of charger.......and maybe it's got something to do with the design for a deep discharge battery.......but I've done this now for maybe 15 years, and I'm only on my 3rd battery now.
Like I say, I have no clue about any of this.