Energy harvesting wireless sensor network nodes would not be able to operate without duty cycling. In TinyOS, duty cycling is supported through Low Power Listening or LPL. LPL is sender-centric: the longer the wakeup interval, the more power a receiver saves, at the cost of more energy per transmission for the sender. Due to the limitations of energy storage technologies, there is a limit to the sender wakeup interval which energy harvesting senders could support. Currently, the limit could be derived computationally or experimentally. Computational derivation is overly conservative, while manual experimentation is labour intensive. In this paper, we present a protocol which enables sensor nodes to determine the wakeup interval limit experimentally without human intervention or the aid of other nodes. Not only does the protocol allow for easier determination of the said limit, it also allows network nodes to adjust to environmental changes that nodes encounter while in deployment, such as capacitor ageing.