San Diego, March 16 -- A jury has decided Apple should pay $31 million in damages for infringing on patents for technology owned by mobile chip maker Qualcomm that helps iPhones quickly connect to the internet and extend their battery life.

The verdict Friday in a San Diego federal court follows a two-week trial that pitted two former allies that have become bitter adversaries. The trial is a fragment of a legal battle involving Apple and Qualcomm, which are sparing over who invented some of the technology used for key features in smartphones and other mobile devices.

The stakes will be much larger in another federal trial next month that will determine whether Apple should be required to pay Qualcomm for licensing other technology used...