It is a charger, but instead of being a "trickle" or "float" charger, it drops into "maintenance" mode after the battery is fully charged so it will not damage the battery if left connected long-term.What does a battery tender do? Is it like a charger?
Depends: if it is a good one it will have the correct temperature compensation to always hold the battery at the correct voltage. Lead acid batteries need a negative tempco, lower set voltage at higher temps. I think the right set voltage is 14V (+/- 0.5V) at about 25C, and the tempco compensation has to adjust the set voltage about -12mV/C.my friend just gave me a batery tender with no instructions. how do they work just atatch the leads and plug in? are you suposed to leave on all winter? will it overheat the batery? thanks.
From the spec sheet on this one:
One model is temp compensated, I assume the others are not. I would not leave any charger on a lead-acid battery continuously if it doesn't have this feature.TEMPERATURE COMPENSATION (BT PLUS Only): The output
voltage is compensated at -3.5mV/ °C/Cell. This increases the output voltage
in cold climates to keep the battery from being undercharged and, more
importantly, reduces the voltage in high temperature climates to protect the
battery from overcharge.