Verifying battery condition by looking at ones headlights is useless. Headlights take about ten amps. A starter easily takes 200amps. A voltmeter across the terminals while attempting to start is the way you verify the battery isn't the issue. When the battery stays at 12+ volts and there is no crank, it isn't the battery. The next step is to see if the 12+v at the other end of the battery cable (the starter) is also staying at 12+v. If it doesn't the voltmeter needs to move up the circuit to the battery and find the resistance.

If it does then the term 50 activation signal needs the same evaluation. A dead battery jumped to start a car will get you nowhere if the alternator isn't supporting it.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician