It is a huge challenge to run IoT devices/sensors powered solely through ambient harvested energy. Since the harvested energy is less and is stochastic in nature, it is extremely challenging to achieve low latency and high reliability. To this end, we propose a distributed, energy-management module called ReNEW, using Constructive Interference (CI) to achieve our target of increased reliability, especially in the low harvesting regimes. We choose CI-based protocols to leverage low latency guarantees. Specifically, we propose a Markov-Decision model to maximize the energy utility in the infinite horizon by allocating energy optimally using a threshold-optimal policy. Since an energy scheduler is insufficient we propose distributed techniques to conserve energy on redundant nodes in the network, and dynamically activate them based on feedback. We implement ReNEW on Indriya and FlockLab testbeds for real-world scenarios in a network of 20 source nodes out of the 30 nodes. ReNEW collects data periodically with 2.5 times higher packet reception compared to LWB when the harvested energy is as low as 50μ J/s for 100B packets every 30s with a saving of 25% higher residual energy. In a nutshell, by integrating ReNEW with CI based protocols, we enable guaranteed latency and increased reliability in battery-less devices/networks.