Future RFID technologies will go far beyond today's widely used passive tags. Battery-powered active tags are likely to gain more popularity due to their long operational ranges and richer on-tag resources. With integrated sensors, these tags can provide not only static identification numbers but also dynamic, real-time information such as sensor readings. This paper studies a general problem of how to design efficient polling protocols to collect such real-time information from a subset M of tags in a large RFID system. We show that the standard, straightforward polling design is not energy-efficient because each tag has to continuously monitor the wireless channel and receive O(|M|) tag IDs, which is energy-consuming. Existing work is able to cut the amount of data each tag has to receive by half through a coding design. In this paper, we propose a tag-ordering polling protocol (TOP) that can reduce per-tag energy consumption by more than an order of magnitude. We also reveal an energy-time tradeoff in the protocol design: per-tag energy consumption can be reduced to O(1) at the expense of longer execution time of the protocol. We then apply partitioned Bloom filters to enhance the performance of TOP, such that it can achieve much better energy efficiency without degradation in protocol execution time. Finally, we show how to configure the new protocols for time-constrained energy minimization.