I have a
power meter I use to measure how much energy they draw, and a string of 70 doesn't even crack the 2 watt threshold of my device. With about 400-500 lights around my house the total draw is still under 10 watts.
Funny thing- the timer I used to use consumes about 7 watts on its own; so it's less power to leave them on 24/7 than to use the timer.
I also have a string of them that I leave on 365 days per year; tucked into my soffit to give some light to my porch. They have been running for 2 years straight now; so they seem to be durable.