Torre209

So a few days ago I take my 2004 545i out at night come back and all is normal, when I go out the next day to go to my mom for Christmas Eve dinner the batter is dead, completely dead. No doorlocks, no beeping noises, no hazards, not even accessory ignition no lights on screens nothing, it's dead as a door knob, so I jump it takes a sec but works then I notice the radiator fan isn't moving so I go on a quick drive around the block to see if it's going to warm up and come on and nothing. When I got back the fan was still off and now my battery is dead again 😩😩

DanielFD

Your battery is total toast, either that or your alternator. That can affect a bunch of things in the car, wouldn't be surprised its affecting the fan. Have your alternator and battery tested. If you do replace the battery have it coded and registered.

Torre209

Thanks DanielFD, I figured maybe if the battery was toast then maybe it couldnt power the fan because when it first jumped i had to stay in the throttle to keep it from stalling, so i figured it may need spark plugs too because it felt like serious ignition miss but then it smoothed out a little bit, Im nearly certain that i need to do spark plugs to, but if Batt/Alt dont fix the fan what would i do to test the fan before i replace the whole system, are there easily accessible relays/fuses to test it?

Torre209

And why would i need for a battery to be coded/registered? Just some other way bimmer wants to get you or?? Thanks for all the help!!!

DanielFD

Well this has been well documented on the forum. But a fast summary is that BMW opted to use a "smart" battery controller that works with the alternator to prolong the battery life. AGM batteries especially need overcharge protection to prolong the life of the battery. While normal batteries can take the extra load but protection is there also. Coding tells the car what size battery is in and if its AGM or FLA. Registering is telling the car that you changed the battery so that its temperature and charge level can be correctly assumed (thats how it knows when to shut off charge to the battery). Lots of people go on without coding and registering and have no issue. Some people have problems when they dont like the alternator doesn't charge correctly and the battery doesn't last too long. Your choice of what to do. I'd have it coded and registered personally.

Torre209

Any BMW can code it? And do you have any specific battery recommendations? Thanks so much for your help!

DanielFD

Yes any BMW shop can code it, you could get Carly and code it yourself too. Battery recommendations. Well the best battery you can buy. Unpopular opinion but i believe battery brands do matter. It all depends on what available in your area try getting a 95-110mAH battery with 850CCA you'd be getting the best battery for your car. If you can find a Bosch S5 with those specs thats what i would buy.

JPR10

It would make sense to test the battery and alternator. Battery dying or not holding charge can be one or the other (or both).