Instances of batch traffic can be seen in many applications. A set of sensors around the source of a sudden event which try to report it to the cluster head, and energy conserving MAC protocols in hierarchical networks with sleep-awake schedules which lead to burst traffics toward a single destination are good examples. The transient non-stationary nature of network reaction to batch arrivals has led to the development of complex models in order to estimate the network quantities of interest. In this paper, we propose a non-stationary Markov model to capture the transient characteristics of IEEE 802.15.4-based networks response to batch traffic arrivals of one-shot type. Mainly, the slotted CSMA/CA MAC protocol of the IEEE 802.15.4 standard is analyzed and the packet loss metric value is extracted from the proposed model. Extensive simulations were conducted to evaluate the accuracy of the proposed model and to compare its performance with that of the previous models.