We perform general-relativistic simulations of charged black holes targeting GW150914 .
We show that the early inspiral is most efficient for detecting black hole charge through gravitational waves and that GW150914 places only weak constraints on the charge-to-mass ratio , Q / M < 0.4 .
Our work applies to electric and magnetic charge , and to theories with black holes endowed with U ( 1 ) ( hidden or dark ) charges .
With our results , we place an upper bound on the deviation of the so-called theory of MOdified Gravity ( MOG ) from general relativity in the dynamical , strong-field regime .