The installed 12V battery consists of six cans containing positive and negative plates that are dipped in a sulfuric acid solution. The battery's job is to generate current to start the car, ignition, and lighting, as well as for other consumers of electrical energy.
The battery is 100% efficient at 27°C. At -18°C the efficiency drops to 40%. Now, to start the engine, you need more than twice as much energy as you needed at 27°C.
Starting power (starting current) shows the battery's ability to start a car in very cold weather conditions. It shows the current in amperes that the battery delivers for 30 seconds at -18°C without the voltage dropping below 7.2 volts (the minimum level required for a reliable start). The higher this figure, the greater the starting power of the battery.
Backup power shows the time in minutes during which the battery delivers a current of 25A at 27°C, i.e. the time during which the battery provides operation of all auxiliary devices in the car at night and in bad weather conditions with a faulty generator.
In winter conditions at -18°C and below, the battery will charge poorly due to the increase in internal resistance. During short trips in winter, the energy expended by the battery for starting is not restored. As a result, the battery wears out, constantly discharges and eventually fails.
During the summer months, after long journeys, the engine becomes very hot and often difficult to restart. These "hot starts" sometimes require as much power as in cold weather, or more. This is especially true for high-compression engines with large displacements and cars with air conditioning. This again highlights the importance of choosing the right battery for the car's engine.
Purchasing a new battery
Probably the most important thing a buyer should pay attention to is the battery specifications. There are three of them. The first is rated voltage, it is the same for all batteries, and it is impossible to make a mistake. When buying, it is advisable to check the battery with a load fork. The second is capacity, measured in ampere/hours (Ah), means, roughly speaking, the amount of electricity stored in the battery. The capacity determines how long the engine can be turned by the starter, or more precisely, how many attempts to start the engine can be made. The price of the battery is almost directly proportional to its capacity. And the third characteristic is starting current (measured in amperes. A), i.e. the current supplied to the starter during starting. On batteries it can be indicated according to four different systems: GOST (on domestic), EN (standard of the United Europe), SAE (american standard) and DIN. The latter, the German standard, is the closest to our GOST and is set "by default" on most European ones, i.e. when the standard system is not specified. The larger it is, the faster and with greater force the starter will turn the engine.
It is better if you buy a battery with the characteristics specified in the operating instructions for your car: this way it will serve you longer with minimal expenses. You can save money and buy a battery with a smaller capacity, but it will serve you less than the usual term and will not cope well with winter starting. Having bought a battery with even a slightly larger capacity, you will not win in service life, since constant undercharging of the battery will lead to sulfation of the plates, and you will lose money. It is better to change the oil in the engine, and there will be no problems with starting.
The battery must necessarily indicate the country of manufacture and the manufacturing plant, preferably with the address. Secondly, the date of manufacture must be indicated, which is very important if the battery is flooded. Each battery must be accompanied by a technical passport, but the presence of instructions is not required. This is due to the fact that in the West, batteries are almost never sold at retail; they are installed by specialists at service stations. Thirdly, a high-quality battery is unthinkable without a high-quality case, good plugs and smooth terminals, often lubricated with technical protective grease from oxidation and covered with colored plastic caps on top.
(The original material is located on the website «Audimanual.ru»)