I got this because my battery kept dying on me.  I think I found the source of the problem after I ordered it but this thing will make sure my battery is kept at full charge.  It comes with 0-ring terminals and alligator clips.  The alligator clips are very easy to put on the terminals.  I read somewhere that the 0-rings are for motorcycles and lawn mowers and stuff so I will just keep them for that.  Anyways, I used regular jumper cables to give my battery enough juice to start my car.  No where in the instructions does it say if the vehicle should be on or off while charging.  My best guess was off since it takes almost 2 days for a complete charge and who leaves their car on for that long, and plus you can charge it with the battery out of the car.  So anyways, I made that little charge for my battery to get up and running and disconnected the jumper cables.  This next part is very important.  First you should connect the alligator cables to the quick connect ends on the battery charger.  Then put the alligator clips on the car positive/negetive leads.  Then if you used an extension cord like I did, plug that into a socket.  Now line up the charger end with the extension cord end.  Make sure all your connections are well on, and then connect the extension cord to the battery charger.  If all goes well, like it did with mine, the red light should come on and say Charging.  I read somewhere that if both the green/red lights STAY on, that your battery is completely dead and that you should disconnect the battery right away or it could lead to bad damage.  The red/green lights flash at startup but then it turned to red.  So anyways, now I am waiting for the complete charge to fill up my battery.  It is 3pm now on a Thursday and I will fill in this space with when it completed.  Keep in mind the instructions say to keep this charger as far away from the battery as possible while charging.  I have mine on the ground right in front of the car so that should work just fine.  I wouldn't recommend putting it inside the engine anywhere like the instructions say.  All in all, for the money of this thing, it is definately worth having around.  I wish I knew about this when I had my motorcycle, because that thing died on me every other day and the quick connect on this would have made charging that thing a breeze.  Also with a riding mower that won't start.  I might get a socket end for the cord so it can charge while in the car.  Other people have said this in their reviews and I will see what it's all about.  Good luck charging!Edit:  So the cigarette adapter just makes hooking it up easier, but it still needs to be connected to a DC outlet so I will pass on that.  Also, I found out that the unit gets very very hot.  I had it on for like 4 hours and touched it and it almost burned me.  Being close to 90 degrees outside couldn't have helped much either, but just be careful.Edit:  So my battery is fully charged now.  It took about a day to charge the whole thing.  Not bad for a device of this size to charge a full battery that was dead at once.  Very good item, I highly recommend it.