Battery

The battery is the center of the Audi 80 electrical system. Various consumers draw power from its stored energy, and the battery is charged by the alternator.

Operating Principle
The electrode (lead plate) contacts the diluted sulfuric acid (electrolyte) and releases positive ions, that is, electrically charged particles, into the electrolyte under the action of the solution. As a result, an electrical voltage is created between the electrolyte and the lead plate.

However, the voltage produced by the "spontaneous" transfer of charged particles is insufficient, so a charging voltage is applied to the battery. As a result, the lead sulfate of the discharged battery is converted into lead dioxide at the positive electrode and into spongy lead at the negative electrode. At the same time, sulfuric acid is formed again in the electrolyte; the visible sign of the almost completed charging process is the appearance of gas bubbles.

When the battery discharges, the reverse process occurs. The lead dioxide of the positive plate and the spongy lead of the negative plate are again converted into lead sulfate, the sulfuric acid is consumed, and water is formed. Therefore, as the battery discharges, the acid density decreases.

Battery Location
On Audi 80 models with 4- and 5-cylinder engines, the battery is located at the rear right of the engine compartment. On models with 6-cylinder engines, the battery is located at the front left of the engine compartment. At the installation points, it is protected by a cover.

The following batteries are fitted to the Audi 80:

12 V/40 Ah, type number 54045 (all 4-cylinder engines)
12 V/63 Ah, type number 56318 (5- and 6-cylinder engines)

Battery Specifications
Voltage and capacity: in the designation 12 V/40 Ah, the first number (12 V) indicates the voltage. The number after the slash is the current the battery can deliver per unit of time; Ah means ampere-hours. This is the nominal capacity of the battery, measured under standard conditions. In practice, only 2/3 of the stated ampere-hours should be relied upon; for an older battery, only half.

Cold cranking current: the number 220 A or 300 A indicates the current the battery can deliver at a temperature of minus 18°C.

Type number: the five-digit number is used by all German battery manufacturers to identify the battery. For Audi, the corresponding numbers are 54045 or 56318. The first digit (5) indicates the battery voltage of 12 V. The following digits 40 or 63 indicate the battery capacity. The last two digits indicate design features such as model, polarity, gas vent hose and flange.