BMW 528i Electrical problems

Hello to all.
Wondering if ya'll could help. I have a 1999 528i with around 60k miles. Various failure lights have been illuminating intermittently. Airbag, check engine light, seatbelt, etc. Not all of the time...just every once in a while. Additionally, the horn would not work at times and the radio may work but not with the readout. I took it to the dealer and they did a diagnosis and said the battery voltage was too low. Car started fine etc. but the dealer knows best, right? Instead of paying the $250 they wanted to charge for a new battery, I opted to buy and install myself. Anyway, that did not fix the problem. Replaced the battery without plopping on the charger...but it started the car right away. Any suggestions?? It is driving me crazy...Oh by the way this was after a $1000 60k mile inspection.

Thanks ahead of time....

I have the 97 528i around the same milage, the airbag light came on. It must be one of those things. My problem was the sensor (you have plenty of them in your BMW) under the driver's seat and the seat belt latch(also a sensor) went out. total cost of replacement around 400,00 euros which is around 500.00 USD due to the current conversion rate.