Most of the decent newer chargers are microprocessor controlled 2 or 3 stage, and end up in a "float mode" with a maintenance voltage level (around 13.5 volts for a 12 volt battery), and just enough current to maintain that voltage (in the milliamp range). Larger chargers would have 10 or 20 amps, or more, available when "bulk" charging, but still drop to the float level when the charge is complete. The 'tender" class units are usually 1 to 2 amps bulk charging capacity, and drop to the float level for long term maintenance. Battery Tender is sort of the industry standard. The Junior model is .75 amp, and usually recommended for ATV, motorcycle, jetski type applications, though they will float an automotive size battery. You can use a 10 or 20 amp charger with a float mode for maintenance, and you usually can charge a healthy automotive size battery with a 1 to 2 amp tender class unit, but it takes a while. Having one of each type is preferable. Disconnecting lead acid batteries (including the sealed AGM and true Gel versions) and letting them sit, subjects them to internal discharge and sulfation, and, while cold temperature slows battery chemistry and the process, it still occurs. The newer floating maintainers reduce/eliminate this problem. I've tested most of the others, but not the HF unit.
