2001 bmw 525 wagon dead battery issues

It sounds like an alternator related issue. Once the battery drops below 12 volts it will do lots of silly things with gauges and thats why when you change it all works fine. Check that with engine running with a volt meter you have 13.8 to 14.2 volts across the battery, if not you may have an alternator issue

I would make sure that the alternator is charging. It might be that you need a new battery, but without knowing if the car is charging you would eventually have the same issue. Most any parts store can charge and test your battery and tell you if it needs replaced or not, they can also test your alternator to see if it is good. A simple test would be to get a voltmeter or multimeter set for VDC and check between your positive and negative battery terminals with the car running and see if you have more than 12V. If the alternator is charging you should have around 14V.

change alternator

You have a Drain on your Battery. The Nominal drain during the night is 50mA. Anything more than that and you have a issue.

Put a Multi-Meter on your Battery (Between your Battery and your One Terminal's and then one on the Wire itself (Disconnect the NEGATIVE Clamp). MEasure the AMPERAGE DRAW...

Then disconnect one fuse at a time and if the number does not go down. When you get the DRAMATIC DROP, then you have found what system has the draw (test all just for a Piece of mind).

Then once you discovered which system, then you need to dig into that system to define it down to the problem and fix it and then you will have your issue resolved.

Good Luck

my 07 525 xi won't start ether i have change my batteries,start/stop switch,cas board and get new keys 4 months ago and now history repeat its self again

It sounds like that not only is the battery totally dead ,due to a high very internal resistance, but that the alternator has very low output. While car is idling in neutral, the alternator has just enough output to supply the ignition circuits but once in gear and the idle speed drops there is insufficient voltage to run engine so it stalls, It is the same when the lights are turned on as the alternator cannot supply enough to run lights so engine dies without enough drive for the ignition circuits. Try another battery or install a new one. Also have the alternator output checked as it could be the cause of the battery dying in the first place because it has not been maintaining charge as you drive. The alternator problem would be caused by either worn brushes and / or a faulty electonic voltage regulator which is mounted inside the alternator with the brushes.

Welcome to the world of BMW's. return the car to the seller. you got a bad one. You got an electrical short draining the battery. Bring a blank check and sign it over to the dealer. They're going to have to run through the entire electrical system to find the short. That work alone is worth more than the a used up 2001 325i.

first off never never never trust a tow truck driver they are idiots, it takes a BMW 15 mins to go into a sleep mode before a draw can be mesured, as for the dealership they should have caught that using the Midtronics batt/alt tester that is standard from BMW 2.5 years for a batt replacement is reasonable especially in a BMW based on the high demand on the electrical system, I just replaced an alt on an M54 enginge just today so they do go bad, have them give you a print out from the midtronics with your VIN on the printout showing your alt is bad and what the batt is.

sounds like a loose connection in either the battery termanals, the alternator plug or the starter. check and tighten if needed.

i have seen on more than one occasion the new ALT going bad after about a week or so you may want to check your charging system again and see if you can warr out the alt if it is bad