Well Crud! All this talk about batteries has come back to visit me again. I have noticed that my wife's 2008 E60 335i has been cranking kind of sluggish in the mornings. I was kind of suspecting the battery but it was very cold and after starting it on the cold mornings it started fine the rest of the day. Went out is afternoon and hit the starter. It cranked slowly a few times and then stopped turning and all the dash lights went out. I put my jumper box on it and it still didn't do anything but click. I left the jumper box on it for a few minutes and tried starting it again and it fired right up.
I have been noticing that the clock would not keep it's setting for a couple of weeks. I bought a battery from Advance Auto Parts. My cost on it was about $112 and some change, but it is their top of the line battery. It is about 1/2" wider and about an inch shorter than the old one but the counter guy confirmed it three times that this is the right battery. Somewhere around 850-900 amps.
One trick to changing the battery on these cars is to keep a 12 volt source hooked in the system to keep the car from losing its memory. If it loses its memory it will have to be reprogrammed for sure. There is a red plastic cover under the hood that covers a terminal for jumping the car if necessary. What I plan to do is take my jumper box and hook the negative to a metal ground somewhere on the engine and the positive to the terminal underneath the red cover. This will maintain 12 volts to the system to keep the vehicle from losing its memory. Memory being all your personal settings for the radio, clock, seats, vent settings, body control module and PCM. The car can also forget how to idle. These are just a few things that can happen.
Warning! By doing this you will have to be very careful to not let the positive cable terminal touch anything when changing out the battery because it will still be hot. You can take and wrap it with a non conductor type of material until ready to hook it back up. This will save you from having to take it to a dealership to have everything reprogrammed. Be forewarned. This battery can give you a hernia. It is very heavy trying to lift it out of the battery box/trunk area.

Ed

 

This must apply to later models? When I changed the battery in my '05 E60 the car was without power for over an hour while I took the old battery to the store for core value and brought home the new battery and I lost only the clock.

 

With my '05 545i, the multi-cd changer would seem to have to reload/cycle every time I started the car. I had read somewhere that this was a also sign of the battery starting to go.

 

+1. That was the same indication I had only mine started to cycle when the door was opened. Same model.

 

Well, I got around to changing the battery today. Before disconnecting the battery terminals I hooked a jumper box to the RED terminal under the hood and the ground to the engine. If you do it, make sure that you turn the jumper box on. I then disconnected the battery and exchanged it. I didn't have to worry about insulating the positive cable in the trunk. It is surrounded by a large red plastic insulator. DO NOT TAKE ANY OF THE CABLES LOOSE OTHER THAN THE TERMINAL ENDS LOOSE FROM THE BATTERY POST. Otherwise you may loose power to the electronics and loose the memory.
After hooking everything back up I didn't loose anything and didn't have to reprogram anything. The whole job took about 15 minutes. Other than my fingers getting so cold that I had difficulty starting the bolt back in the hold-down strap, it went flawlessly. My car is a 2008. The battery should not have gone bad that quick but it is not covered under warranty.

Ed

 

My battery is 5 years old but I'm not pushing it. I'm due for an oil change in the next week or two, I'm going to have them replace it.
I don't use the dealer anymore but I'm sure I'm looking at $300

 

I also have to change battery shortly and have been looking at the methods described for keeping the electronics with 12v source while battery is being changed. One contributor referred to a jumper box - is this the same as hooking the vehicle up to a low charge battery tender?

 

Probably - if you're connecting it to the + Post under the hood and a suitable ground connection and not directly to the battery terminals in the trunk.

 

i would not connect a charger only. a jump box maybe, since it can act like a capacitor like the vehicle's battery. personally i would just connect the car to another battery/car with jumper cables.

 

I had the same issue, I replaced my battery with an aftermarket battery of the same exact specs for the E60. The vehicle started just fine however I kept getting the "reset date and time" every time I turned off the vehicle and turned it back on. I did read that upon installing a new battery the vehicle had to be programed by the dealer to "learn" the new battery, so that was my next step.

2 days later, somehow the vehicle "learned" it had a new battery and the time reset mgs went away while still maintaining its time settings. If I had to guess, I'd say the computer recognized a constant voltage stream and reprogrammed /reset it self. Its been 2 months since I changed the battery and I've had no voltage/power or Christmas lights issues.