The power and energy efficiency of Field Programmable Gate Arrays (FPGAs) are estimated to be up to 20X less than Application Specific Integrated Circuits (ASICs). What is needed to close this gap is aggressive power/energy savings techniques. Such a potentially effective approach is undervolting, which can directly deliver an order of magnitude static and dynamic power savings. However, aggressive undervolting, without accompanying frequency scaling leads to timing related faults, potentially undermining the power savings. Understanding the behavior of these faults and efficiently mitigating them can deliver further power and energy savings in low-voltage designs. In this paper, we conduct a detailed analysis of undervolting FPGA on-chip memories (BRAMs). Through experimental analysis, we find that lowering the supply voltage until a certain conservative level, V min does not introduce any observable fault. For the studied platforms, we measure this voltage guardband gap to be 39% of the nominal level (V nom = 1V, V min = 0.61V). Further undervolting corrupts some of the data bits stored in BRAMs; however, it also reduces the BRAMs power consumption a further 36.1%. When the voltage is lowered below V min , the rate of these faults exponentially increases to 0.06%, by a fully non-uniform distribution over various BRAMs. This paper comprehensively analyzes the behavior of these faults, in terms of rate, type, location, and environmental temperature.