There is no reason to disconnect anything. In fact, you can even charge the battery from the cigarette lighter if you wanted to and had a suitable plug. Just be careful you get the polarity right. If you disconnect the battery from the car, you will lose your radio code, clock, reset the computer, etc. and the battery will charge a bit faster due to no load on it. If you don't disconnect it these electrical systems will take power from the battery and charger, and you will charge slower.

A car battery is in the neighborhood of 60amp/hrs or so. Charging it at 1/10th capacity is a safe bet. You can use any 12 volt power supply. Just check the amp output of the power supply. Divide the total battery amps but the output of your charger and that should give you an idea of how long you need to charge the battery to fill it up if it was totally empty. For example, if your battery is 60 amp hrs, and you have a 2 amp charger, it would take 30 hours to charge your battery. Of course there are other variables like the current draw of the on-board systems, and the amount of charge left in your battery.

If I was you, I would charge it overnight with something that is not too high power, so , 5amp hrs or less so there is no chance of overcharge. Then, in the morning, if the car starts on its own just drive away and don't worry about it any more. It may take several trips, but eventually the battery will charge fully by itself from the on-board alternator. All you need to do is charge it enough to start the car, and then you are good to go. Do not disconnect the battery to charge it as that only adds more work for you resetting radio code, stations, clock, etc. Just charge it connected and let it take a couple of hours longer due to it being connected -- much easier that way.

Just an an example for you, last winter I had issues with my car where it wouldn't start. I cranked and cranked it until I killed the battery and then I couldnt crank it any more. I put the charger on overnight (it was a 1 amp charger or a trickle charge) while I was working on the car (drying wires and such as it was wet and not starting because of that I thought). Anyway, next day I was able to start it, but the battery was still weak. I drove it around to work and back, and, it took about 1 month of driving to work and back before the green eye on the battery was green again, indicating a full charge. So it may take a while, but as long as it starts and you are driving the car, eventually the battery will get topped off.

Hope this helps!

-=>Raja.

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1983 MB 190E, bought from Germany and shipped to the US in 1986.