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Discussion of BMW's 4th generation E65/E66 7 Series flagship. The E65 generated much controversy, due to its radical styling and iDrive user difficulties. Nonetheless, the E65 broke records to become the best-selling 7-series iteration ever, especially after its 2005 facelift.

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Old 10-17-2019, 02:20 PM
mullioni mullioni is offline
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2007 750Li Completely Dead Battery - Help

I have a 2007 750Li. I replaced the battery a year ago, but failed to run it for several months and the battery is completely dead. I have to manually open the doors/trunk. I tried to jump start it. After connecting to the second vehicle, ( 2009 Lexus 350 RX) the BMW has lights, power door locks, etc., however, after letting it sit connected for a few minutes, it tried to crank over, but sounds like there just isn't enough juice to turn it over fully. If I try to crank it over again, it sounds very weak/almost dead again. After disconnecting, the car is once again "dead".

I have read several posts on here and frankly confused on my next steps. Due to the electronics, I don't want to do something that causes a larger issue.

The battery is a NAPA Legend BAT7549 900A Cold Cranking Amps. It was new in July 2017.

1. Should I have AAA come and try to jump start?

2. Should I remove the battery and have it charged? or charge while connected through the terminals in the engine bay?
If charge - what charger and settings do you recommend?
3. Should I buy a new battery, change out, and then have it registered?
4. Other?

Your help is greatly appreciated!
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Old 10-17-2019, 02:26 PM
Doug Huffman's Avatar
Doug Huffman Doug Huffman is offline
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charge it with a proper AGM battery charger. That means a battery charger NOT capable of more than 4 Amps charging current and not more than 14.7 VDC charging voltage - those are absolute limits for an AGM battery.

A dead 100 AH battery will take more than 24 hours to charge with a proper AGM battery charger! (24 hours X 4 Amps is only 96 ampere-hours.)

The CHARGER I use is a CTEK 4.3 MUS. I use it weekly.

If you have to replace the battery, the ONLY electrical specification that matters is the Ampere-hours Capacity AH. The more the better. And it must be an Absorbed Glass Mat - Valve Regulated lead acid battery with the vent to the outside.

New batteries are not maintained charged on the shelf awaiting sale. Properly bench charge the new battery before installation. A battery will work without registration, but MUST be registered for best service and life.
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Scepticism and Animal Faith (1923)
Scepticism is the chastity of the intellect, and it is shameful to surrender it too soon or to the first comer: there is nobility in preserving it coolly and proudly through long youth, until at last, in the ripeness of instinct and discretion, it can be safely exchanged for fidelity and happiness.
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Last edited by Doug Huffman; 10-17-2019 at 02:31 PM.
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Old 10-17-2019, 02:40 PM
mullioni mullioni is offline
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Thanks Doug. Would you recommend I charge through the terminals in the engine compartment, or should I remove the battery from the trunk and charge externally?
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Old 10-17-2019, 02:55 PM
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Doug Huffman Doug Huffman is offline
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Quote:
Originally Posted by mullioni View Post
Thanks Doug. Would you recommend I charge through the terminals in the engine compartment, or should I remove the battery from the trunk and charge externally?
By procedure, from the underhood terminals in the engine compartment, and simplest. The IBS / BST on the positive red terminal is pretty fragile. The IBS is a 'mechatronic' integrated circuit, and the BST is an 'airbag' without the bag.
__________________
Scepticism and Animal Faith (1923)
Scepticism is the chastity of the intellect, and it is shameful to surrender it too soon or to the first comer: there is nobility in preserving it coolly and proudly through long youth, until at last, in the ripeness of instinct and discretion, it can be safely exchanged for fidelity and happiness.
(The Works of George Santayana p. 65)

Eschew eristical argumentation. I am responsible for what I write, not for your understanding of it.

Last edited by Doug Huffman; 10-17-2019 at 02:56 PM.
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Old 10-18-2019, 02:25 AM
mathat mathat is offline
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after you have charged it for a day - I would test the battery with a volt meter just to insure the battery can maintain a voltage on it's own before trying to start , mine after charging will drop to 12.5v and stay there with the car doing it's usual stuff that drains the battery until it cuts off
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Old 11-04-2019, 06:59 PM
Red.donzi Red.donzi is offline
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I had a new battery installed and did not use car much for 8 months and encountered same fully dead battery. Charged for over 24 hours and was able get car started but continued to get battery error. Had battery tested and came up bad cell. Battery was replaced free but had to pay $80 labor for programming.
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