How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Matt Your Own Question
Matt, Engineer
Category: BMW
Satisfied Customers: 20374
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
Type Your BMW Question Here...
Matt is online now
A new question is answered every 9 seconds

I am ***** *****. I have a 91 BMW 850 with a dead battery.

Customer Question

I am ***** *****. I have a 91 BMW 850 with a dead battery. this car has 2 batteries in the trunk and one is new and the other is apparently dead. I can't get the trunk open because a servo that is powered by the dead battery is not working. How do can I get the trunk open to replace the bad battery, if the bad battery controls the survo to open the trunk?
JA: Thanks. Can you give me any more details about your issue?
Customer: I am looking for an alternative way to get power to the trunk servo. I can't get enough power from the dead battery to do it.
JA: OK got it. Last thing — BMW Mechanics generally expect a deposit of about $18 to help with your type of question (you only pay if satisfied). Now I'm going to take you to a page to place a secure deposit with JustAnswer. Don't worry, this chat is saved. After that, we will finish helping you.
Submitted: 6 months ago.
Category: BMW
Expert:  Matt replied 6 months ago.


I'd start by charging the battery you should be able to do this via the cigarette lighter / accessory socket. You'll need the appropriate attachment for your charger but car accessory shops sell these- Alternatively if you can't get into the car/ boot the other way to do this is jack the car up so you can get under the front.

Locate the starter motor and the large power cable that runs to it - connect the positive battery charger lead to this terminal

then connect the charger negative lead to the metal of the engine block

This should complete the charging circuit and get some power into the battery allowing you into the car

Expert:  Matt replied 6 months ago.


do you still need help?

Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you