What i do is register the number of the car after showing the badge. Its worked OK at the Exeter main hospital for many years but you need to inform them again each 6 Months. The system the fitted with ANPR which would lift the barrier has not worked for many years and the boom has been left up. I have had a lot of visits to this hospital over many years and no ticket so far.
Many years ago in the 1980s, if you were on sickness benefits, you paid to park then go in the Hospital and they would pay you back in cash. I was attending there about 3 days a week back then due to the injuries i had in the 1979 accident