An incoming data packet is received, and a rate of change of residual capacity of a portable power supply is determined. From the determined rate of change it is decided to enqueue or drop the incoming data packet. If the decision is to enqueue, the packet is transmitted. If the decision is drop, the packet is deleted without transmitting. Additional factors may be considered in the decision, such as total energy capacity, residual energy capacity, and first and second derivatives of the residual energy capacity. Real time traffic may be treated differently than non real time traffic, and video enhancement layer packets can be weighted to drop more frequently than video base layer packets for the same flow. If used in the network, congestion probe packets are dropped at a rate matched to the rate at which data packets are dropped to give other nodes an accurate view of link quality.