By studying the in-built storage of an Android smartphone and two Microsoft Surface tablets, a graduate student named Jing Li found that when the devices had their screens off, storage consumed more energy than anything else.
This has implications for users whose screens are off most of the day because, despite their phones and tablets not being in use, their batteries are still being drained, according to the researchers.
Li presented these findings this week at the Usenix Fast Conference and claimed to be most surprised to find software, rather than underlying hardware, was the culprit.
The runtime system, the file system and encryption functions consumed 99% of the energy whereas the remaining 1% was used by the storage devices themselves.
Because portable devices are vulnerable to theft, encryption processes are essential, but they do take a heavy toll on battery life.
The study suggested a partially encrypted file system may be the solution. For example, app developers could pick and choose which data gets encrypted and therefore control how much energy the app consumes.
It also found that power consumption was increased by 18% on the tablets and 102% on the phone by apps that run in secure containers, usually using languages such as Java or Common Language Runtime.
Li suggested shifting the storage tasks like encryption currently running on CPUs to a system on a chip as another way to cut energy use.