Either way works. The "float" charger or "battery maintainer" monitors the terminal voltage, and either turns itself off or reduces the voltage as it senses the battery is getting to full charge. Some trickle chargers just keep on upping the voltage, and they can boil a battery dry over time.
If a battery isn't going to be involved in normal starting and running chores regularly, I like to connect a sealed beam headlight bulb or something similar for a couple of hours occasionally and discharge it a little, then reconnect the maintainer to give the battery a little charge/discharge cycling. There are even solar-powered battery maintainers, if your storage area has access to a window, or is in a carport, etc.
Jerry
