Change your car battery either when there is a defect or when the remaining capacity is no longer sufficient. You can recognise this by various factors:
Engine starting problems
Weak lighting
As the battery is heavily loaded in cold temperatures, a defect is particularly noticeable on winter days. Please note that these starting problems are not exclusively due to the battery. If necessary, contact a garage to check your car.
With normal wear and tear, a battery lasts between four and six years. This value can be greatly reduced by your driving characteristics, such as long periods of standing or frequent short journeys.

Often, with increased capacity, the price goes up. Conventional lead-acid batteries are much cheaper than EFB variants, which in turn are more affordable than AGM batteries.
Often the cost depends on the car. This is illustrated by the example:
Opel Corsa C 1.2 75 hp (55 kW) - from approx. 53 €.
Audi A6 Avant (C6) 3.0 240 PS (176 kW) - from approx. 85 €
BMW 3 (F30) 2.0 136 hp (100 kW) - from approx. 165 €
For small cars with few electrical consumers, small car batteries with comparatively low power and low price are already sufficient. Large cars or modern cars with a lot of electronics not only need more power, but also more expensive battery types due to the automatic start-stop system or brake power regeneration.

For a successful bypass, you first need the appropriate jumper cable and an auxiliary car. This should have a sufficiently charged battery with the same voltage.
The jumper cable usually consists of a black (negative) and a red (positive) cable. You will find all the relevant information about the required procedure in the instruction manual. Pay attention to the following steps so as not to damage the car's electronics unintentionally:
Switch off all consumers and motors
Connect the red cable to the positive terminals of both batteries. First to the donor car, then to the discharged battery.
Connect the black cable to the negative terminal of the intact battery.
Find a ground point with the other end of the black cable, for example the engine block.
Now start the engine of the intact battery and then the car with the discharged battery.
After bypassing, it is important that you remove the cables in reverse order and then charge the battery by driving for a while. If the bypass did not work, either the battery is defective, the cable is not of sufficient diameter or the donor battery is not sufficiently charged.

Both the acid battery and the gel battery are used as vehicle batteries. However, both batteries have different advantages, which I have summarized for you in the following table:
Gel battery
Acid battery
practically maintenance-free
good compatibility
leak-proof
high current output
independent installation position
favourable
Because of its advantages, the gel battery is often used, especially by motorcyclists or campers.

New batteries have a nine-digit number, also called ETN (European Type Number). Among other things, this provides you with information about the cold start current, nominal voltage and the design. If the ETN number of two batteries is the same, you can change them without hesitation.
The numbers are coded as follows:
Digit
Meaning
Definition
1.
Rated voltage
0 to 4 = 6 Volt
5 to 7 = 12 Volt
2. & 3.
Capacity in Ah
63 = 63 Ah
4.
Specification DIN number
0 = Battery already registered with DIN number
1 = New registration
5. & 6.
Format information
Arrangement design
7. & 8. & 9.
Cold test current in amps
Calculate value times 10
Here is an example:
Varta Blue Dynamic 540 125 033
Rated voltage (5): 12 Volt
Capacity in ampere hours (40): 40 Ah
DIN data (125): Battery was newly registered, 25 contains data on forms
Cold test current in amperes (033): 330 A

You can find out the age of your car battery by looking at the date of manufacture. You will find this either on one of the battery terminals or as a sticker on the outer casing.
The installation location of the battery itself depends on the manufacturer and the model. For this I recommend you to read the manual of the car after a visual search. In most cases, the battery is located under the hood.

Old batteries are hazardous waste, which you should take to a recycling centre or workshop if possible. This is highly recommended as batteries are toxic and can harm the environment if disposed of incorrectly.
When transporting the old battery, make sure it is placed on a suitable surface so that it does not fall over.