Here’s a cool site explaining in detail how to run your Christmas Lights off a battery or by using
a DC-AC converter.
When you use a watt of electricity for an hour, that’s a watt-hour, or Wh. An amp of electricity for an hour is an amp-hour, or Ah. Batteries store such a tiny amount of electricity that they’re usually rated in milliamp-hours instead of amp-hours (mAh). 1800mAh is the same as 1.8Ah.
A typical 50-bulb strand of Christmas lights uses 25 watts. So each bulb uses about half a watt. (Remember that, we’ll use it later.) Now we need to see how much electricity is stored in a battery.
A typical rechargeable AA battery (NiMH) puts out 1.2V and is rated at 1800mAh. Remembering that V x A = W, we see that a single battery has a capacity of 1.2V x 1.8Ah = 2.16Wh. But the lights use 25 watts. So you’d need twelve batteries to power your lights for just one hour. Ouch.
You have four options for getting more runtime out of your batteries:
- Use LED Christmas lights instead, such as those made by ForeverBright. LED’s use 80-90% less electricity than regular lights. So your batteries will last up to ten times longer.
- Use fewer bulbs. Who says you have to use 50 lights? Use only 25 and then your batteries last twice as long. Use even fewer lights and get even more battery time.
- Use more batteries. The more batteries you use, the more total power you’ll have.
- Use higher-capacity batteries. NiMH D-cells store up to 11,000mAh. You could also use a small lead-acid battery or a rechargable pack used for camcorders or remote-controlled toy cars.