If you have lost, forgotten or damaged your laptop power supply, you can use batteries to power your computer. Because almost all computers use a power supply to convert 110-220AC electricity to 12 volt DC, you can use batteries, which output power in DC wired in series to meet the voltage to run your laptop. The makeshift charger requires a length of electrical wiring and charged batteries.
Check the electronics label on the bottom of your laptop and note the input voltage. This should be between 10 and 20 volts. It is the voltage that is important to note. For example, the input voltage might be 18 volts DC.
Wire together enough batteries, in series, to meet your computer's requirements. Wiring batteries in series adds together their voltages, while maintaining the current output of the lowest rated source. To wire your batteries in series, connect the negative terminal on one battery to the positive terminal on the next with a short length of wire. Place next to each other two 9 volt DC batteries. Wire the negative terminal on one to the positive of the other.
Connect the batteries to your computer. On your laptop, where the power cord is inserted, there will be an inner contact and an outer contact. The inner is the positive, and the outer the negative. Connect a wire to the open positive terminal on one battery to a paper clip, and the open negative terminal to a wire and a paper clip as well. Carefully hold the positive paper clip to the center terminal on your laptop and the negative paper clip to the outer terminal.
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Hold these two paper clips in place. While you are doing this, the batteries will transfer their charge to the laptop, more slowly than the traditional wall charger, but it will provide enough charge to revitalize a dead battery, allowing you to start your laptop and retrieve any important information.