Battery — general information, maintenance recommendations (BMW 7 Series E38)

The battery installed in the car consists of six cans, in which positive and negative plates (lamellas) are placed, immersed in a solution of sulfuric acid. The main task of the battery is to generate the current necessary for starting the engine, igniting the working mixture, lighting, and also to provide power to other on-board or auxiliary consumers of electricity.

In winter conditions, at temperatures below -18 degrees, the efficiency of battery recharging decreases due to the increase in its internal resistance. During short trips in winter, the energy expended by the battery to start the engine does not have time to recover, and the battery begins to wear out, gradually discharging and, eventually, failing irreversibly.

In summer, during long trips, the engine heats up a lot, and it often happens that it is difficult to restart it. Such "hot" starts sometimes consume no less battery energy than in frosty weather. This is especially true for high-compression engines with a large working volume of cylinders, as well as for models equipped with a k/v system.

For more information about the battery, see Section Checking and caring for your battery Chapters Vehicle settings and routine maintenance.

Purchasing a new battery

The above points to the importance of choosing the right battery, taking into account the engine parameters and vehicle configuration. When buying a new battery, you should pay attention to its performance characteristics:

• Nominal output voltage. It has the same value (12 V) for all batteries used in passenger cars, which virtually eliminates the possibility of error.
• Capacity, measured in ampere-hours (A•h) and, roughly speaking, determining the reserve of electric energy contained in the battery. The choice of the value of this parameter determines how long the battery is able to provide the ability to turn the engine with the starter, or more precisely, how many attempts to start the engine can be made. The price of a battery is almost directly proportional to its capacity.
• Starting current (A), i.e. the current supplied to the starter when starting the engine. The value of the starting current on batteries can be specified according to four different standards: GOST (for domestic batteries), EN (standard of the United Europe), SAE (american standard) and DIN (Germany). The latter, German standard, is closest to the Russian GOST and is indicated "by default" on most European-made batteries, i.e. when the standard system is not specified. The higher the starting current, the higher the speed of the starter and the greater the torque it can transmit to the engine flywheel.

Ideally, the replacement battery you purchase should fully comply with the Specifications in terms of its performance characteristics, which will ensure maximum battery life. Buying a battery with a smaller capacity is hardly a good way to save money, as it will last significantly less and, in addition, may lead to unpleasant troubles associated with starting the engine in the winter. You should not buy a battery with an excessively high starting current - such a hobby is associated with the risk of starting the starter. If the standard battery does not provide proper cranking of the engine, it would be better to first change the engine oil - which will most likely lead to automatic elimination of the problem.



There are several signs by which one can, with a sufficient degree of probability, distinguish an original from a fake. First and, perhaps most importantly: the battery case must indicate the country of manufacture and the manufacturing plant, preferably with the address. Second: the date of manufacture must be indicated, which is of particular importance for sealed batteries (unattended) type. The delivery set must include a technical data sheet, while the presence of instructions is not strictly required. Third: high-quality batteries have a good appearance. The case should have smooth edges, be equipped with reliable plugs and smooth terminals covered with protective caps, which are often coated with a layer of special anti-corrosion grease.

Charging the battery

Charging a failed battery should be done in accordance with the charger manufacturer's instructions.

(You can read the original on the website «BMWman»)