Allow users to enable/disable certain features in order to save energy.
Energy efficiency solutions often provide a tradeoff between features and power consumption. However, this tradeoff is different for different users. I.e., some users might be okay with less features but better energy efficiency, and vice versa.
Allow users to customize their preferences regarding energy critical features. Since this might be more intuitive for power users, mobile apps should provide by optimal preferences by default for regular users.
Consider a mail client for POP3 accounts as example. In some cases, users are not expecting any urgent message and are okay with checking for new mail in no less than 10 minutes for the sake of energy efficiency. On the other hand, there are cases in which users are waiting for urgent messages and would like to check for messages every two minutes. Since there is no automatic mechanism to infer the optimal update interval, the best option is to allow users to define it.