Pretty much all batteries use DC power to charge, but most convert it from an AC power supply. In most cases, 120-volt AC current is run from a wall outlet into a power supply that converts it into low-voltage, low-amperage DC current. A charger that uses a DC power supply instead will usually convert the power into AC, then turn it back into DC in whatever voltage your batteries need.
Instructions
1. Determine the voltage of your power source. DC power supplies vary in voltage. The two places where you usually have to use DC power are in a car and in a boat. A car alternator produces 12 V DC power. Marine batteries often use 24 V DC. USB also uses DC, but it gets that power from a wall socket anyway. If you want to charge batteries indoors where there are wall sockets available, it is more efficient to buy a conventional plug-in charger.
2. Look at the voltage requirements for the battery you are charging. If you are charging the battery on a device that doesn't require you to remove the battery, such as a laptop or cell phone, the output voltage on the power cord is the voltage you need to charge the battery. If you are charging a removable battery, the necessary charge voltage will be written right on the battery itself.
3. Find a charger specifically designed for using the DC power you have available to charge the batteries. Many laptop and cell-phone companies actually make laptop car chargers specifically designed for a particular model or series. In other cases, you can use a universal laptop charger such as the one linked to below. If you are charging your batteries with something other than 12 V or if you can't find a charger for your particular battery, continue to Step 4.
4. Get a DC/AC inverter, which turns DC power into the same 115 to 120 volt AC current that comes out of wall plugs. Follow the links below for car and boat DC/AC inverters.
5. Get a standard AC battery charger and put the battery in. Plug it into the wall and turn it on. Follow the charging directions that come with the charger.
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