It is challenging to design a sensor network if sensors are battery powered. Efficient scheduling and budgeting battery power in sensor networks has become a critical issue in network design. We investigate how energy ratio and the battery ratio, the ratio of initial battery capacities for sensors and cluster heads, affects sensor network lifetime. These results allow the network designer to specify required battery capacities which optimizing energy usage, and therefore leads to reduced total costs for the network which is extremely important in wireless sensor networks.