Patients and visitors must carry loose change for parking at four out of 10 hospitals, data shows.
A third of NHS trusts also do not allow people to pay for parking on exit - leaving them guessing how long they need to stay for.
The RAC collected data under the Freedom of Information Act (FOI) from 164 out of 206 hospital trusts in England, of whom 125 charged for parking.
Some 38% (47 trusts) had no option to pay by credit or debit card at any of their sites, while 32% (40 trusts) do not allow drivers to pay on exit.
Only a third of trusts allowed people to pay by card at all their hospital sites. A further quarter had the facility at some of their sites.
One in three hospitals (32%) allow people to pay on exit - enabling them to only pay for the exact length of their stay - while a further 28% had this on some sites.
RAC spokesman Simon Williams said: "Anyone arriving at hospital, be they a patient or visitor, have far more important things to worry about than paying for parking.
"It is for that very reason that things should be made as stress-free as possible - and that includes taking the pain out of paying to park.
"These figures show that in many cases it is still too difficult for people to pay to park when they make a visit to a hospital in England, with drivers still expected to carry pocketfuls of change in order to park legally.
"This is despite the advent first of credit and debit card payments, and now contactless and mobile payment technology."
He said the new £1 coin would mean many machines need to be upgraded, which "provides a good opportunity for a wider range of payment options to be made available to drivers".
Mr Williams added: "In the absence of free parking at hospitals in England, we believe parking should be made as stress-free as possible for people."
Hospital parking in Wales and Scotland is largely free but patients in England are still forced to pay.
In December, an investigation by the Press Association found that NHS hospitals are making more money than ever from car park charges.
More than half charge disabled visitors and trusts make thousands every year in fines.
Some 120 NHS trusts across England were asked to give figures on parking charges and fines under the Freedom of Information Act, with 89 providing responses.
Overall, NHS trusts netted £120,662,650 in 2015/16 in car park charges, up from £114,873,867 the year before.
Some 27 trusts provided data on parking fines, showing they made £2,300,208 in fines over a four-year period.
In 2015/16 alone, £635,387 was made from fining patients, visitors and staff on hospital grounds.
Health minister Lord O'Shaughnessy said: "Patients and families should not have to deal with the added stress of complex and unfair parking charges.
"NHS organisations are locally responsible for the methods used to charge, and we want to see them coming up with flexible options that put patients and their families first."