Car battery
1. The car battery – the heart of the vehicle electrics
The car battery is far more than just an energy store for the starting process. It supplies all electrical consumers on board – from the interior lighting and infotainment systems through to modern driver assistance systems. A reliable starter battery determines whether your vehicle starts safely in any weather and whether comfort functions such as seat heating or the start-stop system work perfectly. It is especially in the cold months that a battery's true performance shows: a high cold cranking current (CCA) and a stable voltage level are crucial when the engine oil becomes viscous and the starter demands more current. In this guide you will learn everything worth knowing about the car battery – from the various technologies and the right choice through to safe replacement and ordering.
The numbers make the difference: a lead-acid battery with 44 Ah and 330 A cold cranking current (EN) is sufficient for a small car without major consumers, while a modern mid-range car with start-stop and plenty of comfort electronics often requires a 70 Ah AGM with at least 680 A. Anyone opting for the particularly light lithium iron phosphate battery (LiFePO4) achieves over 2,000 full cycles – a multiple of conventional lead-acid batteries. All these technical details help you find the right car battery and avoid bad purchases.
2. Battery types and their technologies at a glance
The starter batteries used in vehicles differ fundamentally in design, charge acceptance and cycle stability. The following table summarises the most important parameters. Note that specific values may vary slightly depending on the manufacturer and model. The price ranges given refer to typical market prices in Germany.
| Property | Flooded battery (SLI) | EFB | AGM | LiFePO4 |
|---|---|---|---|---|
| Cycle count (down to 50 % depth of discharge) | 100–150 | 200–300 | 300–400 | >2,000 |
| Cold cranking current (100 Ah) | approx. 450 A EN | 580 A EN | 800 A EN | up to 1,000 A EN |
| Suitable for | Vehicles without start-stop | Start-stop (mild hybrid) | Powerful start-stop, comfort electronics | Lightweight construction, motorsport, off-road |
| Maintenance-free | mostly maintenance-free | maintenance-free | maintenance-free, leak-proof | fully leak-proof |
2.1 Flooded battery (SLI) – classic lead-acid battery
The conventional flooded battery with liquid electrolyte is the cheapest option. Today it is mainly offered as a calcium-calcium version, which has very low water loss and is considered maintenance-free. Typical capacities range between 40 Ah and 100 Ah. The cold cranking current of a 60 Ah flooded battery is around 450 A (EN). This battery is suitable for older models and vehicles without a start-stop function, where only moderate demands are placed on cycle stability.
2.2 EFB battery – optimised flooded battery for start-stop
EFB stands for "Enhanced Flooded Battery" and represents a further development of the classic flooded battery. A polyester fleece on the surface of the plates reduces material abrasion and increases charge acceptance. As a result, an EFB withstands about twice as many micro-cycles as an SLI battery – 200 to 300 are common. In the vehicle, it ensures that the start-stop system starts reliably even with frequent engine shutdowns and that the on-board voltage remains stable.
2.3 AGM battery – powerful for modern vehicles
In an AGM battery (Absorbent Glass Mat), the electrolyte is bound in a glass fibre fleece. This fleece fully absorbs the acid, which makes the battery leak-proof and gives it excellent high-current capabilities. AGM batteries score with excellent cycle stability (up to 400 cycles) and a very high charge acceptance – regenerative braking energy can be recovered efficiently. A 60 Ah AGM often reaches 680 A (EN), a 95 Ah version easily over 800 A. Vehicles with a powerful electrical system and brake energy recuperation rely on AGM as standard.
2.4 Lithium-ion starter battery (LiFePO4)
Lithium iron phosphate batteries (LiFePO4) are increasingly replacing lead technology in the performance and lightweight segment. They often weigh only a third of a comparable lead battery and offer enormous cycle stability – over 2,000 cycles are not uncommon. The cold cranking current is extremely high: a 40 Ah LiFePO4 can deliver a constant 1,000 A, enough for sporty petrol engines and even diesel vehicles with a high compression ratio. Thanks to the integrated battery management system (BMS), the batteries are protected against deep discharge and perform well even at very low temperatures.
3. Important technical parameters – Ah, CCA, dimensions
- Capacity in ampere-hours (Ah): The stored energy. A 60 Ah battery can theoretically deliver 60 A for one hour. This value, in combination with the vehicle's electrical system, determines how long consumers such as a parking heater or radio can be operated when the engine is off.
- Cold cranking current (CCA/EN): The maximum available current at -18 °C for a duration of 30 seconds without the voltage dropping below 7.5 V. Expressed in amperes (EN standard) or CCA (SAE). An AGM with 760 A EN provides enough power for a large-capacity diesel in winter, while a flooded battery with 330 A EN is sufficient for a small petrol engine.
- Dimensions and terminal arrangement: Standard groups such as H5 (LN2), H6 (LN3) or H7 (LN4) have defined length, width, height and terminal position. An incorrect terminal height or reversed polarity can lead to a short circuit. The dimensions must match your vehicle exactly – the onboard power supply control unit expects the correct battery size.
- Resting voltage and state of charge: A fully charged 12 V battery shows around 12.8 V. At 12.2 V the charge is only 50 percent, below 11.8 V the battery is considered deeply discharged and must be charged as soon as possible.
4. Which car battery fits my vehicle?
The right choice does not depend on price alone, but on the requirements of the vehicle. Check the following criteria:
- Note the original battery specifications: In the vehicle handbook or on the old battery you will find the type, capacity (Ah) and cold cranking current (A). These values should be met at least, or better slightly exceeded.
- Start-stop technology: With start-stop systems, switching to EFB or AGM is mandatory. A simple flooded battery would fail prematurely within a few months.
- Installed comfort electronics: Many assistance systems, auxiliary heaters and audio systems with high current demand require a powerful AGM with high cycle stability.
- Space conditions: Pay attention to the standardised battery boxes. An entry in the parts list or a professional assessment prevents installation problems.
For a Golf VII with 1.6 TDI and start-stop, for example, an EFB battery 70 Ah / 640 A EN is specified, while the same platform with a full assistance package and recuperation requires an AGM 68 Ah / 680 A EN. An older Opel Corsa B without start-stop, on the other hand, is satisfied with a 44 Ah flooded battery (330 A EN).
5. Installation, polarity and replacement of the car battery
5.1 DIY vs. workshop – what should be considered?
The battery replacement can be carried out yourself with a little manual skill. However, mistakes – such as the wrong terminal order or improper disconnection – can damage the onboard electronics. Especially in vehicles with a battery management system (BMS), the new battery often has to be registered. Incorrect registration can lead to malfunctions of the energy management and impair comfort as well as starting ability. We therefore recommend comparing the options in our detailed guide: Replacing the car battery yourself or workshop.
5.2 Step by step: replacing the car battery
Anyone carrying out the replacement themselves should follow this sequence:
- Switch off the engine, remove the ignition key, deactivate consumers.
- Disconnect the earth cable (negative terminal) first. This avoids short circuits when loosening the positive terminal.
- Loosen the positive cable. Remove the fastening screws and, if applicable, the retaining bracket.
- Remove the old battery. Lift the heavy battery out straight, pay attention to your posture.
- Insert the new battery, secure the holder.
- Connect the positive terminal first, then the negative terminal. Ensure the terminal clamps are correctly seated and apply sufficient corrosion protection with terminal grease.
- Function check: Starting the engine, checking the onboard voltage and, if necessary, reinitialising window regulators or clocks.
For vehicles with TPMS sensors (tyre pressure monitoring system), it is often necessary to relearn the sensors after a battery change – provided the sensor battery itself is not flat. You can find out more here: TPMS sensor guide.
6. Charging and maintaining the car battery correctly
Regular care significantly extends the service life of your starter battery. Especially in winter, when short journeys dominate and many consumers are running, the battery is only insufficiently recharged. A microprocessor-controlled charger with an IUoU characteristic ensures that the battery is safely fully charged and precisely maintained in trickle mode. For flooded batteries, a charging voltage of 14.4 V is recommended, for AGM usually 14.8 V. Lithium batteries require special chargers with a LiFePO4 characteristic and a final charging voltage of 14.6 V. You must never overcharge a deeply discharged battery with jump starting without subsequently charging it fully – otherwise sulphation and loss of capacity may occur.
Always store a battery in a cool and dry place and charge it fully beforehand. Recharging every six to eight weeks is advisable to compensate for self-discharge. An AGM loses about 3 % of its capacity per month; a lithium battery only around 1 %.
7. Buying a car battery online – advantages and what you should look out for
Buying a car battery online offers several advantages: a large selection, transparent technical data, the option to compare prices and reviews – and, in the case of Electronicx GmbH, fast, predictable delivery. The guide Buying a car battery safely online gives you all the tips for a safe order. We ship your new starter battery free of charge with DHL within Germany – so the goods reach you quickly and reliably.
When ordering, full compatibility must be ensured: capacity (Ah), cold cranking current (A), terminal polarity and design must match your vehicle exactly. In our shop you will find the common brands and technologies with all the data you need. If you are unsure, our customer service will help at [email protected] or by phone on +49 7135 7194106.
8. Frequently asked questions about the car battery
How do I recognise that my car battery is getting weak?
Typical signs are a delayed starter when starting (a "cranking" sound), flickering headlights with the engine running, a battery warning light that stays on permanently, and the failure of electrical comfort functions when the engine is off. Measure the resting voltage: below 12.2 V with the consumers switched off, the battery is already heavily discharged.
Can I replace an AGM battery with a flooded battery?
No, that is not technically advisable. Vehicles fitted with AGM at the factory have a battery management system that is tuned to the higher charging voltages and the special charging characteristics of AGM batteries. A normal flooded battery would be overcharged there, age prematurely and could become dangerous in extreme cases. Always replace an AGM with an AGM, an EFB with an EFB, and a lithium battery only with the vehicle manufacturer's approval.
What should I do if the car battery is deeply discharged?
Charge a deeply discharged lead battery immediately with an intelligent charger that is suitable for the relevant technology. Fast chargers without automatic switch-off can damage the battery further. If the voltage can no longer be raised above 10 V, there is probably irreversible sulphation or a shorted cell – the battery must then be disposed of and replaced. With lithium batteries, the BMS prevents deep discharge; should it nevertheless occur, contact the specialist dealer.
How long does a car battery last?
The average service life is 4 to 6 years. This depends heavily on use: frequent short journeys, extreme cold or heat and a permanently high electrical load can shorten the service life. An AGM battery can reach 7 years under good conditions, lithium batteries often 10 years and more.
Which car battery do I need for my car with start-stop?
For most start-stop systems, an EFB or AGM battery is specified. Look in your vehicle handbook for the recommended specification. Important: even if an EFB was originally fitted, you can often upgrade to a higher-quality AGM, provided the dimensions fit and the vehicle electrical system supports the higher charge acceptance. A pure flooded battery is ruled out in principle.
Is a lithium starter battery also reliable in winter?
Yes, modern LiFePO4 starter batteries are equipped with an integrated heating system or temperature-stable management and deliver sufficient cold cranking current even at -20 °C. The BMS ensures that the cells are protected against frost damage. However, the purchase price is higher; the investment pays off above all with a high cycle requirement, weight saving or vehicles with extreme short-journey profiles.
How do I dispose of an old car battery?
Car batteries must never be put in household waste. Hand the old battery in at a specialist retailer or at a municipal hazardous waste collection point. In Germany, retailers are obliged to take them back – as are we: after buying a new one, you can return your used starter battery to us. We take care of environmentally sound recycling.
What polarity does my car battery have and why is it important?
The polarity describes on which side the positive and negative terminals sit – usually referred to as "polarity 0" (positive right) or "polarity 1" (positive left). Swapped terminals can cause serious damage to the vehicle electronics and short circuits. Before buying, always compare the position of the terminals with your old battery or the vehicle manufacturer's specifications.
9. Electronicx GmbH – your partner for car batteries
Electronicx GmbH from Cleebronn (Baden-Württemberg) specialises in car batteries, TPMS sensors and vehicle electronics. Our range includes flooded batteries, EFB, AGM and lithium starter batteries from well-known manufacturers. We offer you personal advice, reliable delivery and a transparent service.
Electronicx GmbH
Hindenburgstr. 37A
74389 Cleebronn
Germany
Phone: +49 7135 7194106
Email: [email protected]
Managing Director: Andreas Emschanow
VAT ID No.: DE300176428
Stuttgart Local Court HRB 752730
If you have any questions about choosing the right battery or about your existing order, you can reach us by phone and by email. We look forward to helping you.