How to replaced the battery
Owners Manual? Did you open the trunk? Remove the battery cables, negative first, lift out, put new battery in, connect positive then negative. There might be a vent tube on it as well that will need to be reconnected. Reset the stations on the radio, window settings and maybe the headrests.
Would suggest the person hook up a battery charger or similar device to maintain current to the system while changing the battery.
Search Mercedes-Benz SL-Class Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Mercedes-Benz SL-Class Experts