The minimum power allocation strategy for the repetition-based amplify-and-forward (AF) relaying scheme given a required symbol error rate (SER) at the destination is first derived. We consider the scenario where one source and multiple partners cooperate to transmit messages to the destination. The power allocation strategy that demands the minimum transmit power of all cooperating partners is described and analyzed. However, this power minimization strategy does not necessarily maximize the lifetime of battery-limited systems. Then, we propose two other AF cooperative schemes to exploit the statistical channel state information (CSI), the residual battery energy, and the quality-of-service (QoS) requirement. It is shown that the network lifetime can be extended considerably by taking all these three factors into account.