The brief
Mr Joseph sent his 220i in for a normal service, and the battery test that's part of it detected a worn battery, slow to crank and on its way out. He had it changed while the car was in. On a BMW a battery change is never just a drop-in, the new one has to be registered with IBS, the battery management system, so the charging system knows it's fresh and charges it correctly. 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 slow cranking and odd electrical behaviour. A worn battery doesn't recover, so it needs replacing with the correct type, and registered with IBS so the charging looks after it from the start.
The diagnosis
The service check went through everything and the battery test had it down, failing the load test and unable to hold voltage, the alternator charging fine. The brakes, belts, hoses and underbody checked out, no fault codes stored otherwise. So it was a battery replacement, the correct type and rating, fitted and then registered with IBS so the charging would look after it properly.
The work
The old battery was removed and a new genuine BMW battery of the correct type and rating fitted, the terminals cleaned and the clamp torqued properly. The new battery was then registered with IBS 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, and the electrics behaving normally.
The outcome
Strong starts, steady voltage, the electronics back to normal, and the new battery registered with IBS so the charging system manages it. The 220i went home sorted. A worn battery turns into a no-start, and on a BMW the new one has to be coded in, so catching it on the service and changing it properly headed that off.