Black hole X-ray binaries (BH XRBs) can launch powerful outflows in the form of radio-emitting discrete ejecta, which are generally observed to be produced during bright outburst phases, at the transition between different accretion states. However, little is known about the energy, the powering mechanism or the composition of these jets. Covering the entire trajectory of these objects with radio-interferometric observations is fundamental, as it allows us to model their motion with great accuracy and, hence, to constrain their physical parameters. In particular, observing the jet's final deceleration phase, often poorly sampled, is crucial to obtain a reliable estimate of the jet's energy. In this context, I will present results on the modeling of the motion of the relativistic ejecta from two BH XRBs: MAXI J1348-630 and MAXI J1820+070, which launched some of the most spectacular jets observed in the recent years, both detected at large scales as they decelerated interacting with the ISM. We modelled the entire motion of the jets with a full dynamical model based on external shocks, which provided us with constraints on the jet's Lorentz factor, inclination angle, mass and kinetic energy. Thanks to the dense coverage of the jet deceleration phase, our results support the finding that these objects are launched with an initial kinetic energy that is far greater than what commonly inferred from their synchrotron emission, as well as showing that BH XRBs appear to be mostly located in low-density environments.