I have a 95 BMW 530, last summer I didn’t drive my car for a few weeks. When I tried to start it the battery was dead. I replaced the battery. Whether I drive or not, the battery drains in about a week. Any ideas? How do I test the alternator? Could I have bought a bad battery?
To test the alternator, take a volt/ohm meter and set it to read 20 VDC. Place the leads of the meter on the battery posts and take the battery voltage reading. It should be 12.3-12.6 volts. If the reading is below that the battery is discharged. Now start the engine and with leads of the meter still on the battery posts, measure the alternator output voltage. It should read 13.5-14.5 volts. If the meter still reads the battery voltage and begins to drop, the alternator isn’t functioning.
Tester
It sounds like there is an excessive parasitic current drain on the battery while the car is parked. I suggest you have a shop check the electrical system out for that and also have them do a load test on the charging system. That will tell you how good the system is working.