you can't charge a 12 volt battery with a 12 volt battery, it has to be a higher voltage. they will just level out. this is why your alternator puts out 13.8 - 14.4 volts.
example: charge a 12 volt battery which is sitting at 0V with a 12 volt battery which is fully charged at 12V. one will discharge down to 6V, the other will charge up to 6V, then there will be no potential difference, nothing more will happen. (basic example, not incredibly specific)
haha, after typing that, i re-read and you said supply. not totally sure but since the supply is constantly putting out 12V, the battery should charge up to or just under 12V, depending on how much of a load the battery creates for the supply.
also, i'm pretty sure there has to be more circuity involved, you can't just hook them up directly, you'll burn something up.
yea... besides using a little wall plug would take a while to charge maybe a week... just go spend 30$ on a battery charger.. or hook it up to another car
it's a risky thing... youl need to make your own charging circuit than just running a plug to the battery and a couple of transistors... youll need to dig out wireing diagrams from somewhere
you should be able to hook the resistor and diod in series with the line hooked to the positive battery post. no need for a transistor, i don't know what good that would to. just make sure all components are within specs so they don't just burn up.
to use a wall outlet just use a trickle charger. do NOT try to build a bridge rectifier and use power resistors to trim the voltage. All you'll do is blow up the battery or cause it to gas. You need to trickle charge a lead-acid battery at a slower rate so it doesn't expand and gas, which by the way can kill you.