Conventional battery-less energy harvesting systems typically operate with predictable energy sources. In case of an unpredictable energy shortage, they are not able to execute tasks properly or retain data. Prior battery-harvester based architecture suffer from inefficiency for highly energy-constrained energy sources. This paper presents a battery-harvester dual-path energy management unit that enables separation between the idle mode energy path and active mode energy path to tackle the challenges of unpredictable low energy sources. The simulation results indicate an average improvement of 70% in the battery power usage and 20% in the available active time as compared to the conventional battery-harvester energy harvesting system. The proposed energy management unit will be of benefit to future energy harvesting systems with low and unpredictable energy sources.