  We present the asymptotic solutions for spacetimes with non-zero cosmological
constant $\Lambda$ coupled to Maxwell fields, using the Newman-Penrose
formalism. This extends a recent work that dealt with the vacuum Einstein
(Newman-Penrose) equations with $\Lambda\neq0$. The results are given in two
different null tetrads: the Newman-Unti and Szabados-Tod null tetrads, where
the peeling property is exhibited in the former but not the latter. Using these
asymptotic solutions, we discuss the mass-loss of an isolated
electro-gravitating system with cosmological constant. In a universe with
$\Lambda>0$, the physics of electromagnetic (EM) radiation is relatively
straightforward compared to those of gravitational radiation: 1) It is clear
that outgoing EM radiation results in a decrease to the Bondi mass of the
isolated system. 2) It is also perspicuous that if any incoming EM radiation
from elsewhere is present, those beyond the isolated system's cosmological
horizon would eventually arrive at the spacelike $\mathcal{I}$ and increase the
Bondi mass of the isolated system. Hence, the (outgoing and incoming) EM
radiation fields do not couple with $\Lambda$ in the Bondi mass-loss formula in
an unusual manner, unlike the gravitational counterpart where outgoing
gravitational radiation induces non-conformal flatness of $\mathcal{I}$. These
asymptotic solutions to the Einstein-Maxwell-de Sitter equations presented here
may be used to extend a raft of existing results based on Newman-Unti's
asymptotic solutions to the Einstein-Maxwell equations where $\Lambda=0$, to
now incorporate the cosmological constant $\Lambda$.
