My personal interpretation of the concepts of "tender" and "trickle charger" are as follows (and I don't fool myself into believing it's the same as everyone else, much less any sort of industry standard):
Tender: an automatic charging device that will charge only as needed
Trickle Charger: A device with a low-amp output...low enough to not overcharge even if left "on" at all times.
My experience is that the HF trickle chargers CAN bring back batteries with a low charge...if the battery is otherwise still good. I'm talking about the AC powered ones...not the solar DC ones.
Just another reference point.
Clem
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.
B02S4
Reader
2/4/09 5:44 p.m.
stuart in mn wrote:
...I should mention I do have a namebrand Battery Tender. I tried it once, and the damn thing cooked my car battery dry....
Almost anything can malfunction. I personally have more faith in Deltran than I do in HF. That said, did your situation occur 31 years ago, or more recently?
B02S4 wrote:
stuart in mn wrote:
...I should mention I do have a namebrand Battery Tender. I tried it once, and the damn thing cooked my car battery dry....
Almost anything can malfunction. I personally have more faith in Deltran than I do in HF. That said, did your situation occur 31 years ago, or more recently?
It was two or three years ago.
In reply to Rorence:
How useful is it in a canoe? 
