For a hydrogen-like ion of atomic number $Z$, the ground-state energy is:

For a hydrogen-like single-electron ion of charge $+Ze$, $E_n = -13.6\,Z^2/n^2\,\text{eV}$. The ground state has $n = 1$ so $E_1 = -13.6 Z^2\,\text{eV}$. For example $\mathrm{He}^+$ ($Z = 2$) has a ground state energy of $-54.4\,\text{eV}$.