in FeynRules [@Alloul:2013bka], and use MadGraph[@Alwall:2014hca] for event generation, Pythia [@Sjostrand:2006za] for hadronization, and DelPhes [@deFavereau:2013fsa] for detector simulation. Fig. \[fig:prod\] shows the pair-production cross-section of the charged singlet Higgs as a function of its mass for four different center-of-mass (c.m.) energies at the lepton colliders. Here we consider the scenario of minimal mixing of the singlet charged scalar for this figure. The charged Higgs decays to a charged lepton and a right-handed neutrino and gives rise to a final state of dileptons with opposite charge ($l^{+}$ and $l^{-}$) and missing energy. Even the case where the charged Higgs is a mixture of $\d^\pm$ and $H_L^\pm$, this is the only kinematically allowed 2-body decay channel with its branching into 3-body decays being almost negligible. This is because $H_L$ does not couple to the quarks or leptons and its other physical states (the charged state with $H_L^\pm$ and $\d^\pm$ orthogonal to the one considered here and the CP-odd and CP-even neutral states coming from $H_L^0$) are much heavier. Schematically, the signal looks like $$\begin{aligned}
e^+ e^{-} \rightarrow H^{+} H^{-} \rightarrow l^{+} l^{-} \cancel{E}_T+ X,\end{aligned}$$ where $l^{\pm}$ is either one of $e^{\pm}$, $\mu^{\pm}$ and $\tau^{\pm}$ or combination of them. Inside the detector 