Vehicles driven by combustion engines are equipped with a 12 volt Battery. The battery is commonly a lead-acid SLI type. It is box shaped and typically measures 25 cm x 20 cm x 18 cm in size and weighs around 16 kg. The 3 Series BMW box is constructed of heavy plastic. This battery provides the electrical power to run the systems on the vehicle when the engine is not running and provides the power required to start the engine.
The battery is usually housed in the engine compartment under the bonnet. On some car makes and models it is housed under the rear passenger seats or in the boot.
Wherever the 3 Series BMW battery is housed it must be securely fixed. In the designated space there will be a specific tray/base plate for the battery to sit in. There are various types of clamps and brackets to hold the battery securely in place. Some are long ‘J’ bolts which are hooked at one end and threaded at the other. The hooked ends connect to the base frame and the threaded end slots through angled top brackets which are tightened to the top edges of the battery with nuts, this clamps the battery down on the base plate, holding the battery in a firm position. Some vehicle, makes and models employ a series of flat brackets that clamp the battery to the base plate using the bottom lip at the base of the battery.
Problems with the 3 Series BMW brackets and clamps, requiring them to be replaced, are usually due to corrosion issues.