  We present a novel certified model order reduction (MOR) algorithm for
switched descriptor systems applicable to large-scale systems. Our algorithm
combines the idea of [Hossain \& Trenn, Technical report, 2023] to reformulate
the switched descriptor system as a switched ordinary differential equation
with jumps and an extension of the balanced truncation for switched ODE from
[Pontes Duff et al., IEEE Trans.~Automat.~Control, 2020]. Besides being the
first MOR method for switched descriptor systems applicable to the large-scale
setting, we give a detailed numerical analysis by incorporating the error in
the computation of the system Gramians in the a-priori error bound for the
output of the reduced system. In more detail, we demonstrate, theoretically and
numerically, that the standard error bound is not applicable, and a certificate
must account for the numerical approximation errors.
