MakingTo create a battery charger, you will need a power source that will output voltage equal to the battery voltage. For example, since most automotive batteries are rated at 12 volts, a 12 V DC power supply is needed to charge this type of battery.
To connect the electrical leads from the battery to the DC power source, you will also need clamps that are large enough to fit on the electrical terminals of the battery. Typically, you can find a 12 V DC power adaptor and clamps--such as large alligator clips--at an electronics store (such as Radio Shack in the U.States. or Maplin in the U.K.). You will also need a pair of electrical pliers, a soldering iron and some solder.
To create the battery charger out of a DC adaptor, cut the connector end of the adaptor, and strip the cable of about an inch (2.5 cm) of insulation. Pull the two wires apart until each wire is separated from the other by about a foot (0.3 m). Attach the one wire to one large alligator clip by soldering the wire to the alligator clip terminal. Attach the other wire to the other alligator clip by soldering the wire to the terminal of that alligator clip.