Car Charger on, drains battery?

[GrayWhale]

Does keeping a car charger constantly connected when it's not charging, drain the battery?

And can I charge the battery using this A/C charger while running something connected to the battery?

This one:   http://www.harborfreight.com/quickview/index/index/id/9741/

 

[Optimistic Paranoid]

Many boats have marine battery chargers permanently mounted and hard wired to the battery bank.  When they dock, they plug the boat into shore power and it starts recharging the battery automatically.

Can't tell you anything about the HF.

 

[Trebor English]

These days small portable chargers have a microprocessor chip and some LEDs.  If you leave it unplugged from 120 and connected to the battery it will drain.  If it is a motorcycle battery it will matter.  If it is a huge 8D battery it won't matter much but then it won't be enough of a charger either.

If you believe that the microprocessor knows about charging stages like bulk and float and keeps track of that then adding a load to the battery would confuse the computer.  I have not seen that problem.  I don't think the chargers are any smarter than they used to be except for the part about turning on.  If there is no battery or the battery is reversed it won't charge.  If the battery is discharged to 6.5 volts I have seen chargers decide it is a 6 volt battery and only charge it up to 7.

 

[SternWake]

Yes, it certainly can, but it might not. Only proper tools placed inline can say for sure.

Time is a consideration too. if only a day or two any small parasitic load is no real issue, but weeks or months, parasitic loads will overdischarge batteries seriously compromising their capacity if one can even get them to accept a charge afterwards.

In general, best to unplug 'smart' chargers from both AC and DC when not in use.