[b_t_s]

"so it will eat twice the battery" may be nearly true on headless boxes running CPU heavy workloads. Mobile apps are about as far from that as you can possibly get. Sure it's probably a measurable impact, but I would expect it's less of an impact than things like how bright the backlighting is, whether you keep GPS usage to a minimum, how well you minimize and batch network communication, etc, etc. CPU is a small part of a phone's power budget and mobile apps spend a lot of time with the cpu largely idle.