Battery Replacement 850i

[DanMar]

Hi,
I'm new to the Forum so it'll probably seem like it - my apologies.

I have a 1991 850i. I've experienced recurring battery drain. After having my batteries discharged and recharged so many times they won't hold a charge.
I'm ready to replace them, but I don't want to scew something up. Are there any special things I should be aware of? Do I need to only disconnect one at a time?
Is there an order in which the 2 batteries should be removed/re-installed? I heard somewhere that there's a cutoff switch when you're not going to be driving the vehicle for a while - if it exists can you tell me where it is?

Any help you can provide a newbie would be much appreciated.

DanMar

[8Harry8]

Just ask Roger for the cut-off-switches!

Welcome to the forum BTW and always start disconnecting with the "ground's"!

- - - Updated - - -

Hey man, you're gonna hear this a lot. But this forum has a search button and it's a pretty good source, especially something that's been beaten to death like this. And every time you throw up a thread like this, it will pop up when someone does use the search function for "battery replacement." Not to be rude, but it's just a waste of time. But regardless, removing the batteries shouldn't be a problem; I usually disconnect the negative terminal than the positive and make sure the cords don't make contact with the car.

Dominies art ;-)
Always the same 1st abate, takes so much longer to type it than to find and offer the right link!

[Ahmed303]

Dan,

I recommend that you find the source of the drain first. My guess would the GM capacitors which is a very economical fix.

Once you solve the drain issue, you will not need the cutoff switch. However if you still want cutoff switches there are various types available that you can use the search function of this forum to find. As far as order of removing batteries, there is none. They are connected on parallel and thus it does not matter.

Here are some pictures of my old cutoff switches but I got rid of those when I replaced the batteries with larger ones.

Old Batteries





New Batteries

[Timm]

Here's the replacement procedure:

http://www.meeknet.co.uk/e31/E31_Bat...eplacement.htm

[DanMar]

Thank - very helpful - particularly the pictures.
On the cutoff switch I guess you just had it hooked up to one battery.
Does the cutoff come with a wire from the positive side over to the cutoff?
In your picture it looks like the equivalent of another terminal head on the same
side as the negative terminal.

Again, sorry for questions that are probably obvious to many, but I'm a work in progress.

Dan,

I recommend that you find the source of the drain first. My guess would the GM capacitors which is a very economical fix.

Once you solve the drain issue, you will not need the cutoff switch. However if you still want cutoff switches there are various types available that you can use the search function of this forum to find. As far as order of removing batteries, there is none. They are connected on parallel and thus it does not matter.

Here are some pictures of my old cutoff switches but I got rid of those when I replaced the batteries with larger ones.

Old Batteries





New Batteries

[TxGR8White]

while you are at it, get the biggest battery you can stuff in there (INTERSTATE MTP-93, DURALAST 49L, or equivalent), the mounting holes are already there.
Just remember to disconnect the NEGATIVE first, then positive, remove batteries. Connect the POSITIVE first, then the negative - this will keep you from being unwittingly introduced to the principles of Arc-Welding...

[rockytt]

this will keep you from being unwittingly introduced to the principles of Arc-Welding...

My 10mm craftsman wrench has a 1/4" chunk missing in the middle from the time I forgot that very important lesson while removing the battery from my 914/6! Every time I pick up that wrench I have a very obvious reminder to remove the correct cable first...

[TxGR8White]

My 10mm craftsman wrench has a 1/4" chunk missing in the middle from the time I forgot that very important lesson while removing the battery from my 914/6! Every time I pick up that wrench I have a very obvious reminder to remove the correct cable first...

Especially with a pair of those MTP-93's - they are rated at 1000 amps each!
Remember, it isn't the voltage, it is the amperage that will kill you....

[EEDegreeToDrive]

Hi,

I have a 1991 850i. I've experienced recurring battery drain. After having my batteries discharged and recharged so many times they won't hold a charge.

Dan,

I recommend that you find the source of the drain first. My guess would the GM capacitors which is a very economical fix.

It is certainly possible that your batteries are shot, but it is much more likely that your general module is not shutting the car down properly. When the general module fails (from 20 yr old capacitors), the current drain typically kills the battery in about 3-4 days. (Do you hear relays clicking and have strange behavior of your wipers/windows?)

http://forums.bimmerforums.com/forum...-Module-Repair

As long as your batteries are less than ~8 years old, and haven't spent too much time dead/flat, they should still hold a charge if you correct the underlying current drain. Additionally, Sears has an inexpensive battery maintainer ($20-30) that can de-sulphate a "dead" or comprimized battery, but it takes several days to do so. FYI, The battery in my E32 lasted about 10 years; I haven't had the E31 that long, but the PO replaced the batteries twice because of the bad general module.

Especially with a pair of those MTP-93's - they are rated at 1000 amps each!
Remember, it isn't the voltage, it is the amperage that will kill you....

Tx, In this case, what will kill you is the explosion and fire, not the current. It only takes a few milli-amps to kill someone under the right conditions. However, because the resistance of the human body is several K-ohms, you need 100+ volts to conduct enough current to make a difference. http://www.hubbellpowersystems.com/l...07-0801-02.pdf

Additionally Direct Current is much less likely to cause a severe problem than AC. 25Hz is worst, 50hz in Europe and Asia pretty bad, 60Hz in the US is slightly safer. At lower AC frequencies and high enough currents, your muscles lock-up, and you are unable to move, then your heart stops. With DC, you can usually pull your arm back. In other words, you can put your hands across car batteries all day..

Back to the OP though, you can remove the batteries in any order you want. Aside from the obvious mistake of shorting your wrench from +12V to ground, the additional problem (in the 8 series) with removing the positive first is that the +12V terminal is still energized after you take it off the first battery. Regardless, it is always safer in the 8 to remove the grounds first.

Also, if you ever need to cut the power to the car, the easiest place is the one shared ground terminal on the driver's side.

[Ahmed303]

Get the biggest battery you can stuff in there (INTERSTATE MTP-93, DURALAST 49L, or equivalent), the mounting holes are already there.

Agreed. That's what I did as you can see from my pictures (Interstate MTP-93 to replace the MTP-91). Make sure you vent them correctly.

[waterhead]

Current will kill too. I've been bit by 19,000v low current uamp. Hurt like hell. I work on equipment that had 5v 75amp circuit, we avoided at all cost.
We work on a UPS that has 48 car batteries in it...that makes me nervious to work on. Lighting in a cabinet!!!

[Fatandre]

How much cranking amp does the 850 need?

[dragon850]

How much cranking amp does the 850 need?

700 is best.

[NevadaMike]

Don't forget to get the radio code before you disconnect the batteries. You will need the code to unlock the radio after the batteries are disconnected. If you don't have it you will have to go to the dealer to get it. Also you should perform the DK (throttle) motor synchronization procedure after the battery replacement.

[slainerf]

How do you get the radio code?
Second. What the DK ... can you please explain and provide info? I am changing my batteries too
Thanks
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[bdiefAZ]

I run a single H8 AGM battery in my car, several others here in AZ have done the same.

To do this: verify and disconnect the cross-cable that connects the + terminals on the batteries.

[ulflei]

The radio code you can get for free from your dealer or there are several companies on the internet helping you for a small fee.

[PabloRock]

Second. What the DK ... can you please explain and provide info?

The DKs are basically the throttle bodies, one for each bank. Fuel is controlled electronically (fly by wire. the 850 was one of the first with that). They do tend to get dirty over time and may need to be cleaned if you are having throttle issues. (I haven't cleaned mine, but there are write ups on how to do it and think there is one in the DIY section). They are connected directly to the intake manifolds right in the front of the engine.

[slainerf]

I run a single H8 AGM battery in my car, several others here in AZ have done the same.

To do this: verify and disconnect the cross-cable that connects the + terminals on the batteries.

Could you post pictures or video showing what u did? Thanks


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[bdiefAZ]

The single battery conversion has been done on several e31’s in AZ, both V8 and V12 models.

Here are the steps towards single battery conversion on the e31:

1. Disconnect both batteries from vehicle: (Driver side Negative, Passenger side Negative, Driver side Positive, Passenger side Positive - in that order for safety)
2. Remove both batteries from the vehicle
3. Locate the positive cable that connects both batteries. The connection point is located on the passenger side positive battery terminal. (red arrows shown in image indicate positive connection cable) Verify cable with multi meter. Remove Cable or wrap and label both ends for reference.

e31 battery cross cable.jpg

Fasten your new H8 AGM battery into passenger side battery well and secure the battery with factory hardware. Clean terminals and battery posts, then attach positive cable, followed by the ground cable to the battery.

The driver’s side battery well can be used for tool bag storage on road trips to maximize space in trunk. I used a 15 inch tool bag from the hardware store.

IMPORTANT NOTE: Prior to single battery conversion, ensure that the car’s electrical health is strong, including:
· a strong alternator
· fresh fuses (including the 2 hidden fuses near the battery)
· good electrical ground strap on the engine to chassis
· rebuit general module with fresh capacitors
· removal of phone module/harness, CD changer if not used, and EDC module/relay if system is no longer present

If your car is 1994 or newer, I would also suggest either: removing the alarm siren, replace siren with a new unit, or potentially replace internal batteries. The siren;s internal batteries go bad with time, and have the potential to drain your car’s main batteries and trigger false alarms. The siren is located under the passenger side windshield cowl and can be accessed with the cabin air filter housing removed. Alarm siren shown is the later model siren with internal batteries, earlier cars had a simple horn and this does not apply.

e31 alarm siren.jpg

[slainerf]

The single battery conversion has been done on several e31’s in AZ, both V8 and V12 models.

Here are the steps towards single battery conversion on the e31:

1. Disconnect both batteries from vehicle: (Driver side Negative, Passenger side Negative, Driver side Positive, Passenger side Positive - in that order for safety)
2. Remove both batteries from the vehicle
3. Locate the positive cable that connects both batteries. The connection point is located on the passenger side positive battery terminal. (red arrows shown in image indicate positive connection cable) Verify cable with multi meter.

e31 battery cross cable.jpg

Fasten your new H8 AGM battery into passenger side battery well and secure the battery with factory hardware. Clean terminals and battery posts, then attach positive cable, followed by the ground cable to the battery.

The driver’s side battery well can be used for tool bag storage on road trips to maximize space in trunk. I used a 15 inch tool bag from the hardware store.

IMPORTANT NOTE: Prior to single battery conversion, ensure that the car’s electrical health is strong, including:
· a strong alternator
· fresh fuses (including the 2 hidden fuses near the battery)
· good electrical ground strap on the engine to chassis
· rebuit general module with fresh capacitors
· removal of phone module/harness, CD changer if not used, and EDC module/relay if system is no longer present

If your car is 1994 or newer, I would also suggest either: removing the alarm siren, replace siren with a new unit, or potentially replace internal batteries. The siren;s internal batteries go bad with time, and have the potential to drain your car’s main batteries and trigger false alarms. The siren is located under the passenger side windshield cowl and can be accessed with the cabin air filter housing removed. Alarm siren shown is the later model siren with internal batteries, earlier cars had a simple horn and this does not apply.

e31 alarm siren.jpg

Thanks for the post. Now to be sure I dont screwed up.
1. Looks like the only thing here is just to install a new AGM battery in the passenger side? That it?
2. I just got back my GM with new resistors, and mine is 91 so no issues with the horn batteries.
3. Now, what do you do with the battery cables/connectors of the driver side? Do u wrap them in electrical tape?
Sorry if I sound stupid but I am new to my e31.
Thanks


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[slainerf]

Could you post pictures or video showing what u did? Thanks
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Hello again, now I got confused. Here you said to disconnect the cross connector from both batteries but the write up you posted doesn't say that...
So the connector showed in the picture of the write up is the connection that needs to be disconnected?
Are u still installing the new battery in the passenger side?
Thanks


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[slainerf]

Ok thanks for the info

[Kimolaoha]

Re. mystery battery drain, is the old stock cellphone or any of its original wiring or trunk brain box still in the car? Mine had not been completely removed and caused a battery drain issue until I finally found and pulled the correct fuse back in one of the trunk arrays. I posted about this here years ago in case you want to look. This issue seemed to manifest itself by an odometer that was illuminated even when the car was shut down. It went away after that fuse was pulled, but not immediately - maybe a week or so - so maybe there is/was a capacitor involved. Maybe worth a look.
Here it is: https://www.bimmerforums.com/forum/s...2#post27892252

[slainerf]

Re. mystery battery drain, is the old stock cellphone or any of its original wiring or trunk brain box still in the car? Mine had not been completely removed and caused a battery drain issue until I finally found and pulled the correct fuse back in one of the trunk arrays. I posted about this here years ago in case you want to look. This issue seemed to manifest itself by an odometer that was illuminated even when the car was shut down. It went away after that fuse was pulled, but not immediately - maybe a week or so - so maybe there is/was a capacitor involved. Maybe worth a look.

Could u post a pic of the fuse you removed? I got the car last year drive twice. Drain the batteries and was doing the crazy stuff the car does when GM issues. I got the GM fixed and hopefully it fix the problems. But I will like to take a look of what u mentioned. So if u can post any video or pics explaining or showing that fuse please.


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