I am completely unfamiliar with our MB electron ignition system but I have had some experience with antique vehicle electronic ignition conversions. A Petronix ignition system which uses a hall effect module requires an input voltage of >4.3 volts to function. If our MB ignition system functions in a similar manor your battery output might be below the required potential needed for ignition to occur.
I would replace the battery, thoroughly clean the cable connections, and change both the cam and crank sensors with Bosch replacements.