Batteryless network nodes could enable unprecedented ubiquitous sensing applications, while gathering energy from the environment and hence removing maintenance costs for batteries. However, these devices inherently suffer frequent power failures and reboots, due to the volatility of the incoming energy, thus classical synchronous message passing cannot work. On the other hand, the asynchronous scheme is not viable either, since power outages can occur at different rates on two devices, and for unpredictable lengths of time. In order to align wake-ups of wireless nodes, a non-canonical mechanism to keep track of time must be devised. We present a novel architecture for reliable packet exchange between energy-harvesting devices, resilient to power failures and agnostic about the physical layer. The proposed architecture, implemented on real hardware, shows an improvement in throughput of a factor of 10, and reduces energy waste by 33 % to 78 %, as compared to the asynchronous message passing.