The brief
The C200 had a tired battery, slow to crank with the lights dimming at idle, and the owner wanted it replaced with a genuine Mercedes battery rather than a cheap aftermarket one. That's the right instinct on a modern Mercedes: the battery has to be the correct AGM type, fitted properly, and registered to the car, and a genuine part with the right rating does that job and lasts. The battery starts the car and steadies the voltage for everything electronic while it runs. They wear out, the capacity drops, and once it can't hold a proper charge you get the slow starts and odd behaviour. The new one has to be registered to the car's energy management so the charging system knows it's fresh and charges it correctly. A worn battery doesn't recover, so it needs replacing and coding in.
The diagnosis
A battery and charging test confirmed it, the battery was down, failing the load test and unable to hold voltage. The alternator was charging fine, it was just the battery at the end of its life. So it was a battery replacement, a genuine Mercedes AGM battery of the correct type and rating, fitted and then registered to the energy management so the charging would look after it properly.
The work
The old battery was removed and a new genuine Mercedes AGM battery of the correct type and rating fitted, the terminals cleaned and the clamp torqued properly. The new battery was then registered to the car's energy management so the charging system recognised it as fresh, and any stored low-voltage faults were cleared. A quick run confirmed a strong crank, steady voltage, bright lights, and the electrics behaving normally.
The outcome
Strong starts, steady voltage, bright lights, and the new genuine battery registered so the charging system manages it. The C200 went home sorted, the way the owner wanted it: genuine, correct type, fitted and coded properly. A worn battery only fails harder, so changing it for the right one and registering it put the car right.
