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Battery Connection Notes and Replacement
 
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Pelican Technical Article:

Battery Connection Notes and Replacement

Nick Czerula

Time:

1 hour1 hr

Tab:

$100

Talent:

*

Tools:

Set of sockets (10mm, 13mm could vary), flathead screwdriver

Applicable Models:

BMW 323Ci Coupe/Conv (1999-00)
BMW 323i Sedan/Wagon (1999-00)
BMW 325Ci Coupe/Conv (2001-06)
BMW 325i/xi Sedan/Wagon (2001-06)

Parts Required:

Battery, battery vent hose

Hot Tip:

Wear eye and hand protection

Performance Gain:

Car will start well

Complementary Modification:

Replace battery vent hose
Your BMW E46 is equipped with a 6-cell 12-volt lead acid battery. Each cell consists of lead plates in a lattice and completely covered with sulphuric acid (the electrolyte). The chemical reaction between lead and sulphuric acid produces a nominal 2 volts per cell; the six-cells together provide the approximately 12 volts required to operate electrical and electronic components in the vehicle. After the battery is used to start the engine, the alternator (powered via the engine accessory belt) takes over electrical generation and also replenishes the charge that the battery used in starting the engine.

During operation and also during recharging, the chemical reactions in the battery produce heat, which causes the electrolyte (sulphuric acid) to evaporate. The cells in many older batteries are equipped with plastic caps, which allow the evaporated electrolyte to escape. If the level of electrolyte drops below the tops of the lead plates, the plates can become damaged; also the heat in the battery begins to build excessively at that point. If your battery had removable cell caps, be sure to remove them periodically and inspect the electrolyte level. If the electrolyte is at the same level as the tops of the lead plates, add clean distilled water to the battery.

Most modern lead-acid batteries are sealed so that the evaporated electrolyte cannot escape. However, a charging battery also produces hydrogen. This is discharged from the top of the battery using a small vent tube. Make sure the vent tube is not blocked or damaged and keep in mind that open flames or sparks around a charging battery are a potential source of battery explosion. 

Heat, chemical reactions and electrical charges can cause battery connections to become covered with corrosive and insulating deposits. Any time you remove the battery terminals from the battery, be prepared to clean the metal surfaces with a metal brush. A solution of baking soda and water will neutralize acid deposits and clean the top of the battery and the battery compartment.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches. 

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you are working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability. 

Vehicle models change and evolve, as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.
The battery in BMW E46 models is located in the right side of trunk, behind a trim panel.
Figure 1

The battery in BMW E46 models is located in the right side of trunk, behind a trim panel. When replacing your battery be sure to use a high quality unit. Replacing the battery can be done in a short amount of time. Read battery connection notes before disconnecting battery. If you own a convertible E46, you require a different battery than standard models. Convertible model batteries are designed to tolerate the vibrations and movement due to convertible chassis design. Before disconnecting your battery, remove the key from the vehicle and store in a safe place and note any radio presets. When a battery is reconnected or loses its charge the following items may need attention, (depending on vehicle equipment). You may have to reset your clock, enter radio presets, initialize power windows and initialize the sunroof.

Charging Battery: 
You can connect a battery charger directly to the battery or under the hood at the positive (+) and negative (-) grounding point junction.
Figure 2

You can connect a battery charger directly to the battery or under the hood at the positive (+) and negative (-) grounding point junction. The battery junctions are located at right front strut tower (located in green circle). However, I suggest removing the battery from the vehicle when charging. This will avoid filling your trunk with gases the battery emits during charging. Follow the manufacturer's instructions on setting and using the battery charger.

Jump Starting Vehicle:

A vehicle with a discharged battery can be jump-started using a good battery or a good battery in another vehicle. When jump starting: Be sure to work in a well ventilated area, batteries can produce an explosive gas. Wear gloves and eye protection and if battery acid comes in contact with your skin, immediately flush the area with water and seek medical assistance. Move both vehicles close together but do not allow then to touch. Turn ignition OFF in both vehicles. 
Connect one end of positive jumper cable to positive (+) battery terminal of the vehicle with the good battery.
Figure 3

Connect one end of positive jumper cable to positive (+) battery terminal of the vehicle with the good battery. Connect the other end of the positive jumper cable to positive (+) junction terminal (red arrow) vehicle with the discharged battery. You will have to flip open the lid on the positive (+) junction connection. Connect one end of the negative (-) cable to the negative (-) battery terminal of vehicle with good battery. Connect the other end of the negative (-) jumper cable to the negative (-) junction terminal (yellow arrow) of the vehicle with the discharged battery.

Start the engine on vehicle with good battery. Allow it to idle and then raise the engine to 2000 RPM. Next, start engine of vehicle with discharged battery. Once vehicle with discharged vehicle starts, shut OFF any electrical accessories, radio, HVAC blower, etc. Carefully disconnect the jumper cable in the reverse order that you connected them. Allow vehicle with dead battery to idle to recharge the battery.

Replacing Battery:
Working in trunk, lift the carpet up and suspend it using the attached hook on rear of the trunk opening.
Figure 4

Working in trunk, lift the carpet up and suspend it using the attached hook on rear of the trunk opening. (yellow arrow).

Disengage the battery trim cover by twisting the clips 90° counter-clockwise.
Figure 5

Disengage the battery trim cover by twisting the clips 90° counter-clockwise. Remove the battery cover from the vehicle.

Remove the battery fasteners (green arrows) and remove the bracket.
Figure 6

Remove the battery fasteners (green arrows) and remove the bracket.

Using a ratchet and a 10mm socket, disconnect the negative (-) battery cable (green arrow), then disconnect the positive (+) battery cable (red arrow).
Figure 7

Using a ratchet and a 10mm socket, disconnect the negative (-) battery cable (green arrow), then disconnect the positive (+) battery cable (red arrow). Move the negative (-) cable aside and the cover so it does not accidentally come in contact with the battery terminal.

Disconnect the battery vent hose and it lay aside (yellow arrow).
Figure 8

Disconnect the battery vent hose and it lay aside (yellow arrow).

Lift the battery up and remove it from the trunk.
Figure 9

Lift the battery up and remove it from the trunk. Be careful and make sure you have a good grip, the battery is quite heavy. Clean the battery compartment thoroughly.

Clean any corrosion from the battery cable ends if present. Before installing the new battery, check that the battery vent line is not pinched, in good condition and properly routed. Replace if needed. Install the battery in the compartment and attach the vent line. Connect the positive (+) cable. Next, connect the negative (-) cable. Install the battery bracket. Then reassemble the trim cover and the trunk carpet.

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Comments and Suggestions:
NeonCarrot Comments: I'm finding it impossible to remove the battery trim cover - are there any secret clips holding it in
November 16, 2016
  Followup from the Pelican Staff: Should only be the clips shown. Try lifting it out at the spare tire well, angling it out of the trunk trim. - Nick at Pelican Parts  
joe Comments: I have a 2001 BMW 325i. Changed out the battery but then the car will not start...
October 31, 2016
  Followup from the Pelican Staff: Check if you blew a fuse during the repair. - Nick at Pelican Parts  
Greg Comments: My new battery has vent holes on both sides. Do I need to plug the one not connected to the hose or just leave it?
October 29, 2016
  Followup from the Pelican Staff: One has to be plugged, one attached to the vent hose. - Nick at Pelican Parts  
Fab Comments: I have a 325i,the wires for the positive terminal are getting hot to the point it started to melt the sleeves ant idea what may be causing this. I have the correct battery in.
April 24, 2016
  Followup from the Pelican Staff: The alternator may be overcharging. - Nick at Pelican Parts  
PAT Comments: I own an E46, 2004 325i M54 engine. I'm looking to replace the battery and have been told that in order to do so properly I must register the new battery with the car also. this is to assure it functions properly an efficiently. I've also been told that its unnecessary to reprogram the vehicle after changing the battery but necessary to register it. what's the difference ?
October 9, 2015
  Followup from the Pelican Staff: Not on an E46. - Nick at Pelican Parts  
Nick Comments: Hello,
I recently noticed my fan blower motor works when I start the car yet if I turn it off and try to turn it on again it won't work. I replaced the final stage resistor and this problem still occurs. Is it because my battery needs to be replaced or is the fan blower the culprit?
December 3, 2014
  Followup from the Pelican Staff: You didn't mention what vehicle you are working on.

The issue could be the control module for the blower motor. You should check for fault codes. If there are none, check the signal to the blower motor when the problem is present. Is it being commanded on. - Nick at Pelican Parts
 

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Page last updated: Wed 12/7/2016 02:19:20 AM