Smart meters have been widely installed to monitor residential electricity usage worldwide. This brings a serious privacy challenge for the customers, because the meter readings can possibly expose their activities in the house. To address this privacy issue, battery-based privacy preserving schemes have already been studied for several years. In these schemes, a rechargeable battery can both prevent the meter readings from leaking the customer's energy consumption and play a role of saving the cost. However, to the best of our knowledge, none of the existing schemes can achieve differential privacy and cost saving simultaneously. In this paper, we first propose a battery-based differential privacy-preserving (BDP) scheme. We further present two cost-friendly differential privacy-preserving (CDP) schemes by extending BDP scheme. Simulation analyses show that the privacy loss of both CDP schemes are smaller than the existing works. Meanwhile, both CDP schemes stably save the cost under multiple pricing policies.