Printed electronics holds the promise of meeting the cost and conformality needs of emerging disposable and ultra-low cost margin applications. Recent printed circuits technologies also have low supply voltage and can, therefore, be battery- powered. In this paper, we explore the design space of micro- processors implemented in such printing technologies - these printed microprocessors will be needed for battery-powered applications with requirements of low cost, conformality, and programmability. To enable this design space exploration, we first present the standard cell libraries for EGFET and CNT-TFT printed technologies - to the best of our knowledge, these are the first synthesis and physical design ready stan- dard cell libraries for any low voltage printing technology. We then present an area, power, and delay characterization of several off-the-shelf low gate count microprocessors (Z80, light8080, ZPU, and openMSP430) in EGFET and CNT-TFT technologies. Our characterization shows that several print- ing applications can be feasibly targeted by battery-powered printed microprocessors. However, our results also show the need to significantly reduce area and power of such printed microprocessors. We perform a design space exploration of printed microprocessor architectures over multiple parame- ters - datawidths, pipeline depth, etc. We show that the best cores outperform pre-existing cores by at least one order of magnitude in terms of power and area. Finally, we show that printing-specific architectural and low-level optimiza- tions further improve area and power characteristics of low voltage battery-compatible printed microprocessors. Program- specific ISA, for example, improves power, and area by up to 4.18x and 1.93x respectively. Crosspoint-based instruction ROM outperforms a RAM-based design by 5.77x, 16.8x, and 2.42x respectively in terms of power, area, and delay.