I did a tech post on the tech side of the chargers that I harvested off the internet from a tech guy. It's not just about keeping the battery charged, though from a practical stand point you want it to turn your battery over when you want a ride.
Now from memory ( may be poor) the normal chemical reaction that takes place in batteries creates crystals (sulfisication?) and this is what over time causes your plates to short out. The tenders, especially the high ends ones are geared to prevent this or address it while it is occurring when it is plugged in. At least that is what I recall from the information I read.
To the initial post about these Power Outlets, they were pulled off eBay because of a mistake in the pricing. They are top quality BTW. The Battery tender adapter has an outlet adapter (male plug in) on it not just pole ring connectors.
