When compared to apps without ads, the researchers found that apps with ads use an average of 16 per cent more energy.
    
That lowers the battery life of a smartphone from 2.5 to 2.1 hours on average - or down to 1.7 hours at the high end of energy usage.
    
Researchers at the University of Southern California, Rochester Institute of Technology (RIT), and Queen's University in Canada said that a phone's Central Processing Unit (CPU) is like its brain - and ads eat up a lot of that brain power, slowing it down.
    
Apps with ads take up an average of 48 percent more CPU time - 22 percent more memory use and 56 percent greater CPU utilisation (the amount of time the CPU was used).
    
Since the ads themselves are content that has to be downloaded, apps with ads cause smartphones to use much more data - up to 100 percent more, in some cases. On average, these apps use around 79 percent more network data.
    
Together, these frustrations and expenses led users to rate apps with ads lower - costing them an overall average of .003 stars on a five-star rating scale.
    
"In absolute terms, this is very low, but in the crowded and competitive world of apps it's a huge difference. It can make the difference between your app getting downloaded or going unnoticed," said William Halfond, co-corresponding author of the study at the University of Southern California.

Halfond along with Meiyappan Nagappan of RIT and other colleagues compared 21 top apps from the past year – culled from a list of 10,750 that had been in the top 400 of each of Google Play's 30 categories from January to August of last year.
    
They then measured their effect on phones using analysis tools loaded onto a Samsung Galaxy SII smartphone.
    
Next, Halfond said he hopes to create models that will allow app developers to predict how well their products will be received by the public - both with and without ads.