BMW 740i Hybrid High Voltage Battery Replacement Cost

Hybrid vehicles which use internal combustion engines (ICE) and electronic motors must have a storage location for electricity when it is not being used to propel the vehicle. Whether the system uses the ICE and brakes to charge the battery or a combination of the brakes and a power plug, the high voltage electrical battery is necessary to store the high voltage needed to run the large electric motor.

High voltage hybrid batteries are a combination of many individual battery cells. These battery cells are not powerful enough to power a large electrical motor like a hybrid drive motor, but many of these cells put together can drive the hybrid drive electric motor for many miles before needed to be recharged. As the vehicle is driven, the ICE will not only power the wheels, but it will generate electricity for the hybrid drive motor and store it in the hybrid high voltage battery. Also, when slowing down, regenerative braking will develop more power to be stored as electricity in the hybrid high voltage battery. When there is a demand for power, the high voltage battery will discharge into the hybrid drive motor, and this propels the wheels of the vehicle just as the ICE would. In essence, it works as a fuel tank for electricity.

Hybrid high voltage batteries most commonly fail as a result of memory or one or more bad cells. When batteries fail due to memory or degradation of cells the vehicle will loose efficiency (as rated in MPGe). This is because the battery can no longer propel the vehicle with as much energy or for as long as it was previously capable. In some cases, the service hybrid battery (or similar) warning light will display, and the vehicle may no longer be able to drive as an electric vehicle, or even support the ICE with hybrid power. In the worst cases, the vehicle may be completely disabled, even though the 12-volt electronics still function.

Hybrid battery failure requires immediate repair. In many cases the vehicle will need to be towed to a repair facility, and servicing or jumping the vehicle is not possible without manufacturer specific or hybrid drive training.

Hybrid batteries tend to last between 6-10 years on average. There are outliers in both directions, and warranty often covers when they fall below their life expectancy. Although the battery is not serviceable for the typical consumer, they do offer warning signs that service or replacement may be needed soon. When lack of power and decreased fuel efficiency are noticed, the vehicle should be taken for service to test and possibly replace the battery.

Each manufacturer has methodology and equipment to test their hybrid batteries. The results of these tests will determine the serviceability of the batteries. In some cases, individual cells have been replaced to correct a faulty battery, but this is not common professional practice, so the individual cells are not likely to be tested.

Replacing the hybrid drive high voltage battery will be done by disconnecting the 12-volt and high voltage battery in the manufacturer specified manner and order. Once disconnected, protective covers may be used for the battery terminals. The battery access panels, if not already removed, will be removed to access the battery before lifting it out of the vehicle. Since the battery for a hybrid drive system is both bulk and heavy, it is important that the battery be lifted properly, and, in some cases, a hoist be used. Reinstallation requires the reverse of operations, but some software updates and operations may be required.

We do not recommend attempting to service the hybrid high voltage battery. There are may videos of people who have chosen to service these batteries in hopes of saving money, and there are also many failures, injuries, and destroyed electronic components from the same.

The term 'high voltage' is placed around every connector for the hybrid drive system, and the high voltage power wires for the hybrid high voltage battery are typically coated in a very obvious color like red or yellow. This is to prevent the connections, wires, and, generally, any part of the system from being contacted by the consumer. Read the owner's manual before attempting to open the hood or battery compartment. It may prevent serious harm or death.

This repair is not recommended for the DIY mechanic unless the proper high voltage hybrid drive battery service training has been completed. Not only is this a dangerous operation if done improperly, but it can damage many components in the vehicle if service improperly as well.