LEDs are as small as traditional string light bulbs, but they last up to 100,000 hours, use up to 90 per cent less power, and they are almost indestructible under normal conditions. This makes them ideal for homemade battery-powered string lights. The amp-hour capacity of the battery, not the voltage, determines the maximum number of LEDs wired in a parallel circuit. LEDs consume very little current, so a parallel circuit is ideal. Making a light string requires the ability to use a soldering iron and wire-strippers.
Determine the desired length of the string and the number of LEDs to be included in it. Divide the length of the string by the number of LEDs to establish the gap required between the LEDs for a string of equidistant lights. For example, in a 500cm long string containing 100 LEDs the distance between the LEDs should be 500/100, or 5cm. To the length of the light string, add sufficient extra wire to reach from the start of the lights to the battery. Cut two wires to this length.
Strip the insulation from the final 5mm of each wire. Cut the LED legs to the desired length, and then solder the first LED across the ends of the two bare wires. Remember that all subsequent LEDs must have the same polarity, so be sure to note the orientation of the first LED.
Work backward from the end of the light string, removing about 2mm of insulation from each wire at every equidistant point along both wires. Solder one LED across each pair of bared points along the wires. Connect battery clips to the ends of the wires.
Connect the battery clips to the battery terminals, observing the correct polarity. Check the light string for LEDs that fail to illuminate. Identify the "dead" LEDs, disconnect the battery, unsolder the relevant LEDs and rotate them through 180 degrees. Re-solder them, reconnect the battery and check again. Replace any LEDs that still fail to illuminate.
Check the correct polarity of each LED with a 9-volt battery before soldering it to the wires. Solder LEDs quickly using a low-wattage soldering iron. LEDs die if they get too hot.
Never solder a live wire. Doing so may damage the soldering iron and the circuit. Do not wire the LEDs in series. Each LED will consume 12 volts from the supply, limiting a 12-volt battery to powering just one LED.