GEOMETRIC PARAMETERS
The first thing to consider when purchasing a battery is its dimensions. Under the hood of a modern car, there is not much space, and manufacturers design the battery compartment for a specific type of battery. If the old battery was securely fastened with standard mounts when making a purchase, use its dimensions as a reference; measure them. Pay attention to polarity: the positive and negative terminals may be on different sides in various car models and batteries.
The size of the terminals themselves may also differ among different car manufacturers. Terminals are divided into three groups based on compatibility:
Euro. Cone-shaped, externally clamped with a strap, with a diameter of 19.5 mm for the positive terminal and 17.9 mm for the negative terminal. Recessed on the sides of the case to avoid short circuits. The most common type of battery.
JAP. Positive contact – 12.7 mm, negative – 11.1 mm. Terminals protrude above the battery case. Used more frequently in vehicles for the Japanese domestic market.
Screw (American). Instead of clamps, fastenings with internal threads are used. Applied to cars in the United States.
This parameter is more of an additional consideration – terminals can be easily connected using adapters or, in extreme cases, power cables can be modified.
ELECTRICAL CHARACTERISTICS OF THE BATTERY
The primary parameter of a battery is its voltage. In the onboard network of most passenger cars, it is 12V, and the majority of car batteries available for purchase are designed for this voltage. Another important characteristic is the battery capacity, measured in ampere-hours (Ah). It indicates how long the battery can deliver current until complete discharge. The higher the capacity, the more attempts the battery can make to start the car.
When choosing a battery, it’s advisable to refer to the capacity recommended by the vehicle manufacturer. Contrary to common belief, you can install a battery with a slightly higher capacity if the dimensions of the compartment allow. However, selecting a battery with a lower capacity can lead to more frequent and deeper discharges, potentially reducing its lifespan.
There are two types of capacity:
- Nominal capacity, i.e., the capacity of a 20-hour charge. This is usually indicated in the battery specifications (e.g., 6ST-90: a battery with 6 cells, starter type, with a capacity of 90 Ah).
- Reserve capacity, indicating how long the car can run on a single battery charge without being recharged by the alternator.
In addition to capacity, the cranking current of the battery is crucial—a measure of the potential passing through the starter at the moment of engine start. This parameter is often specified on the battery label. It is particularly important for cold weather starts, as tests are conducted at -18°C.
There are three standards:
- EN (European) – discharge to 7.5V in 10 seconds.
- DIN (German) – discharge to 9V in 30 seconds.
- SAE (American) – discharge to 7.2V in 30 seconds.
For example, a marking of 480 A(EN) means that the battery can deliver 480 amperes of cranking current according to the European standard for 10 seconds and then discharge to 7.5 volts.
BATTERY TYPE
Firstly, batteries are divided into maintenance-free, low-maintenance, and those that require maintenance. The latter can be identified by the presence of removable caps. The advantage of serviceable batteries lies in the ability to replace the electrolyte and, often, even the plates. The downside is their rapid discharge, water evaporation, and a shorter service life.
Maintenance-free batteries can operate for up to 7 years; however, they are more sensitive to low discharges, non-repairable, and expensive. Low-maintenance batteries require maintenance approximately once a year, but they do not allow for individual repair of each cell.
Secondly, batteries are classified based on the composition of electrodes. Batteries with liquid electrolyte are divided into:
- Traditional lead-acid batteries: Resilient to low temperatures, resistant to deep discharges (do not have a ‘memory effect’), and cost-effective. Downsides include the need for maintenance and the inability to be inverted. Considered outdated.
- Low-antimony (Sb/Sb): Resilient to deep discharges and voltage spikes. Downsides include the need for technical maintenance and a high level of self-discharge.
- Calcium-based (Ca/Ca): Known for their resistance to vibrations and corrosion, low self-discharge, and minimal water consumption. They poorly tolerate deep discharge (may fail after 3-4 discharges) and are relatively expensive. Maintenance-free.
- Hybrid (Sb/Ca, Hybrid): A hybrid of the two previous types, with low-antimony positive electrodes and lead-calcium negative electrodes. In addition to the qualities of calcium batteries, they exhibit resistance to deep discharge. The downside is their high cost.
- Silver-calcium (Ca/Ag): Made from a lead-calcium alloy with the addition of silver. They have increased resistance to corrosion in addition to all the advantages of calcium batteries. The downside is their very high cost.
Recently, sealed lead-acid batteries with the electrolyte in a bound state have become more prevalent. There are two types of sealed batteries:
- AGM (Absorbent Glass Mat): In these batteries, the electrolyte is contained in a glass fiber mat surrounding each plate. Such batteries are used in vehicles equipped with a ‘start-stop’ system.
- Gel batteries (GEL): In these batteries, the electrolyte is in a gel state.
These batteries are more advanced, capable of delivering higher currents, resistant to discharges, do not evaporate water, and can be inverted without the risk of electrolyte leakage. While their cost is relatively high, they can effectively replace traditional batteries. However, the reverse is true only in extreme cases due to differences in characteristics.
Now you know more about car batteries. You can also find a battery retailer on our MyNextParts service.
Also, if you are going on a long trip, be sure to check the condition of the car along with the battery.
