Battery Maintainence
Battery Maintainence
Electrolyte Level
If battery electrolyte level is allowed to drop substantially, the gas volume inside the battery grows proportionately resulting in an increased amount of flammable gas mixture. Any external or internal spark may result in an oxyhydrogen explosion. Additionally the plates are no longer covered by the electrolyte and may corrode.
As described in SIB 61 01 90, battery electrolyte level should be checked on every Inspection I and Inspection II.
Use only distilled water to top up the battery Tap water and electrolyte must never be used to refill or top off an automotive battery.
Workshop Hint
Electrolyte levels may drop at a higher rate in the winter months, due to higher loads and increased utilization of electrical systems (SIB 61 01 90).
Battery Cable Connections
The top of the battery should be clean. Check for and correct corrosion on the top of the battery and the cable connections.
Workshop Hint
Many battery problems are caused by loose or corroded connections. Insure that cables are free from corrosion and tight before continuing diagnosis.
Battery Charging
The purpose of charging a battery is to put back the energy that has been removed. A battery that is not properly charged will deliver sub-standard performance and display a shorter life span.
A battery should be charged only after performing a visual inspection on the battery case and the electrolyte levels. Never attempt to charge a battery with a damaged case or low electrolyte levels.
A state-of-charge test should be performed before attempting to charge a battery.
Always connect the positive lead of the battery charger to the positive terminal of the battery and the negative lead of the battery charger to the negative terminal of the battery.
Unplug the the charger or turn it off BEFORE disconnecting the leads at the battery.
Batteries that are fully discharged should be charged according to the following table.
The best charging method is to SLOWLY recharge the battery using the BMW approved battery charger.
A slow charging rate allows more time for the electrolyte to penetrate the plates.
Sulfated Batteries
Continuous discharging of the battery or low electrolyte levels cause crystals to form on the plates. These crystals of lead sulphate occur when a battery is discharged. The deeper the discharge the more serious the sulphation. The sulphur molecules that form the sulphate are then absent from the electrolyte, causing the electrolyte to become inefficient.
A battery relies on clean plates and strong electrolyte to both receive charging current and offer strong current discharge. A sulphated battery can do neither Proper recharging of the battery will remove some but not all of the sulphate. Eventually the battery plates are coated with enough sulphate that it is impossible to achieve an efficient recharge.
Testing A Battery for Sulphation
A battery which fails the load test should be tested for sulphation. To test a battery for sulphation, place it on a battery charger for three minutes with the charger set on 40 amps. After three minutes check the OCV if the reading is greater than 15.0 volts the battery is sulphated. Batteries which indicate a sulphated condition should be recharged slowly and retested before being discarded.
Battery Freezing
A fully charged battery can be stored at sub-freezing temperatures with no damage. The battery is protected from freezing to a temperature of -75° F. A fully discharged battery however will freeze at +27° F
Avoid freezing by keeping the battery fully charged.
Carefully inspect a battery which has frozen for a cracked case.
Battery Maintenance (Center Vehicles)
The battery charge is monitored while the vehicle is at the VPC and before it leaves on the transport. When the vehicle is having the QC I performed at the center the check list requires that the battery voltage be checked and maintained to 12.65V minimum.
In order to facilitate tracking vehicles in inventory, BMW has in place a Battery Maintenance Program. The program uses:
- Battery Log Forms
- Battery Log Binder
- Colored windshield stickers (red, green, yellow and white)
The Battery Maintenance Program has three possibilities:
- Vehicle in storage, battery disconnect switch removed
- Vehicle in showroom or display
- Vehicle in storage, Battery disconnect switch left in the vehicle
Vehicle In Storage, Battery Disconnect Switch Removed
A four week charging cycle has been established for these cases. All vehicles arrive with a color coded sticker on the windshield. The color corresponds to the week that the battery must be charged. Also the vehicle will be provided with a Battery Log Form.
The "A" portion (Vehicle Receipt) of the Log Form must be completed during the QC I Display check and then has to be filed in the Battery Charge Log Book under the applicable color coded section. All the vehicles in that color section will have to be charged that week.
Vehicle In Showroom or Display
Because of the high consumer demand on vehicles that are being displayed and not driven, a four week charging cycle is not enough. For vehicles in the showroom the battery has to be charged as frequently as necessary to ensure that the battery never drops below 12.5V Use the "C" portion of the log form (Display Vehicle - Monitored Daily) to keep track of the charging and checking of the battery.
Vehicle In Storage, Battery Disconnect Switch Left In The Vehicle.
Since the battery disconnect switch is left installed and in the "OFF" position the 3 month charge cycle can be used. Use the "D" section of the Battery Log Form to document when the battery is charged.
Upon the sale of the vehicle, the Battery Log Form should be removed from the binder and placed in the vehicle file for future reference.