All modern automobiles use a 12.6-volt primary battery for two primary purposes: to provide the initial current to start the engine and to act as a voltage-buffering reserve, “smoothing” the current flow once the engine is running.
A relatively large amount of current is drawn from the battery when starting the engine. Once started, the alternator replaces the current consumed — usually within a few minutes of start-up and maintains the battery at a full charge.
Many diesel engines use two batteries to meet their higher starting current requirements. Hybrids use a conventional starting battery while having a separate high-voltage battery assembly.
The Cost of Battery Replacement
Why are car batteries so expensive? For one, there is a wide variety of charges for labour costs based on complexity and accessibility. Some batteries are easily accessed in the engine compartment and many shops and even parts houses will replace them at no labour charge.
Some batteries, however, are tucked into fender-wells, underneath seats, and in trunk compartments. Labour costs can run as high as an hour and follow the normal regional pattern: higher costs in metropolitan areas and dealerships, while rural areas and independent shops have lower costs. Expect to pay £0 to £100 for the price range.
In many cases, it is recommended to check the electrical system as a whole when replacing the battery to rule out underlying causes for its failure. This is often done as half-hour labour and is often bundled into the automobile battery price as a replacement package – about £35 to £60, depending on the shop and the region.
The new car battery cost itself is usually the largest component in the service and it can vary from £70 to £260. It can be more on some occasions, like if sourced through a dealership with a significant mark-up.
How to Choose a Battery?
The three main factors in choosing a battery are:
- It must fit the battery tray. The industry uses standardised group sizes so that a new battery will match the old one and install correctly. Sometimes a battery tray will be built to accommodate more than one group size, such as when a vehicle comes with a standard size battery. However, there is a factory option for a larger, high-capacity battery.
- It should have at least the same cold-cranking amp rating (CCA) as the old battery. This is a measure of its ability to provide the initial starting current. A higher capacity battery will have a higher CCA rating. A lower capacity battery may function, but will be working under greater strain than it was designed for and may fail early. In general, a higher capacity battery will perform better and last longer as it will be under less stress relative to its capacity each time it starts the vehicle, and it will have more capacity to spare as it ages.
- Battery warranty is also a factor. A good warranty is usually an indication of good construction. If the manufacturer is willing to offer a free replacement for 18 months, that’s a sign that it is very likely to last much longer than that. After a free-replacement period, batteries usually have a prorated warranty period. This means that the number of months left in the warranty will be calculated and the balance of “value” left in the failed battery will be credited against the replacement cost. Given the need for documentation and the small sums involved by the point of normal failure, prorated warranties are seldom exercised in practice.
Different Types of Car Batteries
Before you go out and buy a new battery for your vehicle, you should first determine which type is suitable for your car. There are basically three types of car batteries for you to choose from: Wet, VRLA, and calcium alloy batteries.
1) Wet Cell Batteries
These are the traditional lead-acid batteries that are mainly used for automotive purposes. Oftentimes, wet cell batteries need maintenance because the water in the diluted acid has to be replaced or topped off from time to time.
Wet cell batteries mainly have two types: SLI and Deep Cycle.
- SLI: These batteries are made for quickly starting the car. SLI means starting, lighting, and ignition, and this type of battery can send fast and powerful waves to quickly power up the vehicle’s engine, lighting, and motor. As soon as the car starts running, it will be sustained by the alternator.
- Deep Cycle: This type of battery is named as such because it can be discharged a great number of times, able to provide energy for long periods, unlike SLI batteries that would definitely be compromised by repeated use. This battery is designed for long-term use.
2) VRLA Batteries
Known as the valve-regulated lead-acid battery, the VRLA is the perfect battery to use in confined and unventilated spaces because it is sealed.
Furthermore, the VRLA battery is considered the safest wet cell lead-acid battery out there because of its inability to leak and release hydrogen gas. Unfortunately, because they are sealed, they can’t really be serviced, unlike wet cell batteries.
There are two types of VRLA batteries, namely the gel cell battery and the AGM.
- Gel Cell – The main difference between gel cell batteries and the wet cell variety is that instead of having the same electrolyte-rich battery fluid, this battery’s cells are covered in a gel-like substance. This substance also contains electrolyte, but the solidity makes the gel cell batteries extremely tough, being able to withstand extremely hot temperatures and physical shock. Furthermore, their solidity makes them immune to spillage as well as electrolyte evaporation. As far as functions go, they don’t differ that much from wet cell batteries.
- Absorbed Glass Mat – This is another dry cell battery that does not employ the use of regular battery fluid. Rather than having flooded plates, the AGM battery has electrolytes contained inside a cluster of thin fibres that form the glass mats.
3) Calcium-Calcium Battery
Just like VRLA batteries, this is a type of sealed lead-acid battery that requires no maintenance whatsoever. This battery makes use of calcium rather than antimony in its plates. This gives the calcium-calcium battery a number of perks, including corrosion resistance, lower self-discharge, and less water usage.
Silver can also be added to the material in the battery to make it more resistant to high temperatures. When this happens, the battery is often called a silver calcium alloy battery.
A 12-volt battery is, by its construction, six 2V batteries assembled in series. Each cell has a set of plates, and these are joined by a bus bar across the top of the plates.
The most common failure is age-related. The plates and the solution they are bathed in rely on chemical reactions to store voltage, and these all break down slowly over time.
Commonly, the expected lifespan of a battery is 5 years, and by the end of that period, it might be noticed that the engine cranks over more slowly. This is usually caused by a loss of cold-cranking capacity due to the plates slowly degrading.
Rapid failures can also occur. When plates degrade, they very slowly shed debris which accumulates at the bottom of the acid bath the plates reside in.
Sometimes this debris can build up enough to contact the bottoms of the plates themselves, leading to an internal short and a slow or rapid loss of battery capacity. This can sometimes draw the battery completely down through internal loss.
Plates themselves can delaminate, crack, or come loose from the bus bar. If this happens in just one cell, it’s called a “dead cell,” and you effectively have a 10.5-volt battery.
Batteries are very resistant to freezing when at full charge, but very easily damaged internally if they encounter freezing weather when discharged. When charged, the plates reside in an acid bath that has a very low freezing point.
When discharged, the solution is closer to water and easily frozen in a way that damages the battery’s plates. It’s a common winter-time problem that a discharged battery, having sat overnight in freezing weather, will no longer take a charge.
Batteries are best tested when at a full charge, which can take an hour or more to achieve, depending on their condition and the charging device used.
A fully charged battery is then tested for its CCA capacity – either with a modern tester that gives a definite measurement or with a load test that simulates the current draw of a starter and looks at how the battery voltage reacts.
A dead cell is usually immediately obvious if present. A battery with an internal draw can, at times, pass both of those tests.
The test for an internal draw is to charge the battery and then let it sit, disconnected. The resting voltage of a good battery will stay at or near 12.6 volts for days. A battery with an internal short will drop slowly in voltage below 12.6 volts, which indicates an internal short.
Other Types of Batteries
Two other battery types commonly used in the automotive industry are gel cells and AGM, or “absorbed glass mat”.
Gel cell batteries use a gelled internal fluid rather than a water solution and are sealed and leak-proof.
By their chemical nature and inherent in their engineering, they work best when used for deep cycle applications (such as electric golf carts or marine trolling motors) where the current is slowly drawn from the battery until it is discharged and then slowly recharged. This kind of cycling can be harmful to a conventional lead-acid battery.
On the other hand, gel cell battery plates can be damaged by the kind of high-load draw that starting a vehicle requires. For the most part, they aren’t recommended as an automotive starting battery.
AGM batteries are an alternative and avoid many of the failures listed above. They use a sponge-like glass mat to separate the plates and carry the lead-acid solution, and they are completely sealed and maintenance-free.
They have a greater capacity than lead-acid batteries to handle high-load starting draws; they lose less current internally over time; and they can be charged more rapidly.
Overall, they are a good choice for automotive use. However, they are more expensive to produce and consequently higher than typical car battery prices, and they have about the same lifespan as a conventional lead-acid battery.
Other Things That May Come Up
A common problem at the time of replacement is corrosion at the battery terminals, which leaves hard deposits on the battery cable ends. These need to be clean to make good contact.
Often, there is not a great deal of metal used in the battery cable ends, and these are easily corroded to the point that they need to be replaced. It is a common recommendation to use anti-corrosive sprays, pads, and greases to prevent further problems – usually around a £14 price-point.
Sometimes, an old battery will leak, which can damage the hold-downs, securing the battery in place and, sometimes, even damage the battery tray or the hardware attaching the tray to the body of the vehicle.
A failing battery can also harm the vehicle’s charging system. If a battery begins with a poor state of charge (or if the battery is dead and the vehicle is jump-started), and the vehicle is started, the alternator then has much more work to do to bring the battery up to a full state of charge.
Combined with the need to run the vehicle electrics, this can over-tax and overheat the component and lead to failure. As well, an alternator that is failing for reasons of its own can damage the battery.
This is one of the reasons that a battery’s replacement labour cost often includes a health check of the vehicle’s charging and starting systems to catch other possible problems at the time of service.
When a battery is disconnected to be replaced, the vehicle’s stored memory may be lost. Radio station presets are the main thing that might be noticed, but many modern vehicles use learned memory for idle speed control and engine running parameters, sometimes even shift points.
These can be lost when a battery is disconnected. When a new battery is installed, everything will still work. However, it may take a few miles of driving before it runs, shifts, and idles just as before. The adaptive memory relearns and relies on preprogrammed parameters in the meantime.
Another feature that some modern vehicles use is battery registration, whereby, upon battery replacement, a scanner must be used to register the battery with the vehicle. It’s not common (mostly on European makes), but it is sometimes an additional unexpected step, without which the vehicle won’t operate.