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Give replacement batteries a bright future

By autotech-nath on March 4, 2021

With battery sales predicted to remain buoyant throughout 2021, Rob Marshall provides an overview of relatively recent battery developments, while focussing on testing and maintenance advice.

Despite today’s 12 volt batteries inheriting the same basic lead-acid principles that were discovered over 160 years ago, numerous minor developments have occurred to increase their lifespans, boost charge acceptance, enhance output and be less maintenance intensive. Many of these changes have continued unnoticed by drivers and technicians alike. This tended not to have any significant consequences, until recently.


Technicians of all ages would have noticed the increasing prevalence of electronic equipment in cars, a trend that has little chance of slowing. While market forces have dictated ever more comfort and safety equipment, environmental pressures are also responsible for vehicle electronics becoming incredibly demanding and complex. The challenge for manufacturers is complying with strict carbon dioxide (CO2) emission limits. CO2, after all, is a gas that is linked directly to fuel consumption: the more fuel an engine burns, the more CO2 results. This is not the same for all gases that emanate from the tailpipe, an important consideration that even some engine tuning specialists are unaware.

Like SLI and EFB batteries, AGM types benefit from being kept above 12.5v state-of-charge. While they accept higher charge voltages, they are less tolerant to overcharging, compared to flooded lead-acid batteries. Check if your smart charger is compatible with AGMs. The pictured charger has a stop-start option, but it is unclear whether, or not, this includes AGMs, so check the instructions if a 14.7-14.8 charge voltage is mentioned or query the vendor/remanufacturer.

As fuel consumption is affected by engine load, it is beneficial to reduce drag on the crankshaft and capture some of the energy that would have been wasted as heat via the friction brakes. This energy can then be redeployed to assist the engine during acceleration. Besides, stalling the engine deliberately, without shutting-down any comfort and safety systems, also aids fuel consumption. CO2, therefore, drops.

Advancing lead-acid battery technology has been crucial to transform such energy and emission saving systems from motor show concepts into realities. While the terminology differs slightly, the ‘traditional’ type of 12v battery powers mainly the starter, lights and ignition circuits, resulting in some battery brands referring to them as ‘SLI’ types. This standard…

As a battery ages and loses its capacity, the internal resistance rises. This means that the car’s charging system must work harder and for longer. The internal resistance also rises as the battery temperature drops, which is another reason why cold weather is especially hard on the electrical system.

…technology is enhanced as a cost-effective means to allow the carmaker to achieve its CO2 targets. The result is the Enhanced Flooded Battery (EFB), which retains the same basic internal construction but EFBs achieve longer life, superior charge acceptance, a 2-4 times superior ability to tolerate deep discharges and a 15-20% higher capacity. Inside, the main differences are a higher number of thinner plates, extra ingredients added to the lead paste material and a reduced electrolyte level. The mats in Advanced Glass Mat (AGM) 12v batteries absorb the liquid electrolyte and are pressed against the positive and negative plates. This deviation in construction reduces internal space further, so that the manufacturer can add more plates without increasing the plastic case’s physical size. AGM batteries are fitted to more sophisticated and expensive vehicles that possess stop-start functions (at the very least). Their advantages include a far higher lifespan, a 30-40% increase in capacity and an ability to withstand deep discharges that are 3-6 times superior to SLI designs.

It is worth noting that, while all of these batteries fit within the 12v category and share the same physical dimensions, the internal differences are what counts. Therefore, never downgrade the technology type, despite the batteries looking the same on first glance.


Batteries suffered during the reduced drive-cycles that resulted from last year’s lockdowns and tier restrictions – and will continue to do so. The leading cause of battery failure is exposure to prolonged periods of charge below 12.5 volts, which encourages internal sulphation that robs the battery of capacity. The lower the voltage, the faster the rate of denigration.

Dead batteries still have a value. Unlike high-voltage batteries, 12v lead-acid batteries are 99% recyclable. Banner Batteries reports that the recycling rate is higher than that for glass and even paper.

Ecobat advises that AGM and EFB batteries are designed to accept higher voltages from their smart alternators. Therefore, the energy needed to start the engine can be replenished within several minutes, instead of ~20 mins for a SLI battery being recharged by a conventional constant voltage (14.4v) alternator. Naturally, this means that AGM batteries can also accept a higher charge rate, when connected to a main- powered charger.

GS Yuasa agrees but adds that both automotive and motorcycle AGM batteries benefit from a higher recharge voltage, such as 14.7V – 14.8V, compared to 14.4v for SLIs. Yet, AGM batteries do not possess liquid electrolyte that can absorb and disperse heat. This means that AGMs are more sensitive to overcharging and this explains why they tend not to be installed within an engine bay but in an alternative location that is less exposed to heat from the engine and exhaust systems. Yet, should you discover an AGM battery beneath the bonnet, ensure that all of its protective shields and covers are intact. When using a smart charger, choose one that possesses AGM-compatible algorithms to ensure a slightly higher charge voltage and prevent overheating damage.

Attending a 12v battery training course is worthwhile. GS Yuasa reports that it is putting together an ambitious plan to raise awareness of its academy, to ensure as many of its resellers as possible can access its training courses. It reports that it also aims to grow its IMI accreditations, while developing the course contents.


If a customer covers a low mileage, you might be asked for your recommendations on home charging. As it can take around 20 minutes, or approximately 10 miles, of driving to replace the energy used to start the engine, a sound means of identifying whether, or not, home charging is necessary is to see how many miles the vehicle covers between MOT tests. Ecobat suggests that a car covering fewer than 70-90 miles and more than 15- 20 journeys per week indicates a low mileage user. This means that the car is not being driven sufficiently long for the battery to be recharged. Should you be asked about where a smart charger should be connected, consult the car manufacturer’s handbook, or that of the smart charger. With AGM and EFB batteries especially, do not recommend old-style trickle chargers, which tend not to switch-off and risk overcharging.

A faulty charging system will, obviously, reduce the battery’s state- of-charge. A quick check of alternator voltage under load is a wise idea but remember that smart alternators do not work on fixed voltage principles and checking them is more involved.

Should your customer use the car for multiple short runs, Ecobat warns that you should suspect battery voltage walk- down. This is energy that is taken from the battery, which is not replenished fully, prior to the next engine restart. While you can recharge the battery in the workshop (ideally overnight), you may have to advise that the customer either drives the car for longer distances, or invests in a smart charger for DIY home charging. This not only gives them a degree of protection against a potential non-start situation but the exercise also prolongs battery life, by keeping its voltage above 12.5v.

Should a tested battery display a low voltage but refuses to accept charge for long, Ecobat advises that you check the warranty time scale, or advise the customer to do so, if it looks relatively new and you did not supply it. Ecobat is one such company that tests every battery returned under warranty. Note that ineffective charging and parasitic drains will discharge and damage the battery, so a technician is wise to check for these issues, using a DC clamp meter, to see if the car is demanding excessive current after its various ECUs have shut-down. If the fault exists within the car and not the battery, expect a battery warranty claim to be rejected.

Once the battery is charged fully, you should check its state- of-health. This is measured in amps and compare the resultant figure against the battery’s CCA rating, which should be displayed on its case. In most cases, CCA cannot be replenished by recharging, although some smart chargers possess desulphation modes, which may help to restore some CCA, caused by the battery suffering a short-term sub 12.5 volts drop in its state-of-charge.


Even the best quality batteries cannot tolerate poor storage conditions between manufacture and installation. Quality battery manufacturers advise factors on how to store batteries so that they are delivered to the technician in the best possible condition, before installation. However, some garages possess a battery stock either to use within the workshop, or to sell direct to the public. An appreciation of how batteries should be stored is useful, for which we are grateful to Varta especially for its recommendations.

While battery state-of-charge below 12.5 volts affects capacity negatively while fitted to the car, the same is true in storage. It is wise to develop a process to ensure that any stored batteries have their state-of-charge analysed periodically and…

Banner Batteries comments that its sales have remained buoyant during the winter period and sales are exceeding forecasts. It is confident that demand levels will continue to remain healthy in 2021, a stance echoed by GS Yuasa. Apart from the unique issues caused by COVID-19, Banner Batteries also references the trend that the public is holding onto cars for longer.
When checking battery state-of-health, compare the amps reading against the CCA figure on the battery case. This may be specified as Starting Power and will be presented in Amps: 780A in this case.

…charged (but not overcharged) when appropriate. As self- discharge rates (and, therefore, battery ageing) increase with temperature, batteries are best stored in a cool atmosphere between 15 and 20 o C. The electrolyte can also freeze and crack the case but this risk is unlikely to pose a problem, provided that the optimum state-of-charge is maintained.

When in storage, keep the battery away from strong sunlight, not only because of increasing internal temperatures but also it risks UV degradation of the plastic case. The oldest stock should be used first, in a first-in, first-out system, and note the maximum storage time indicated on the battery. Take care during handling and, to prevent the possibility of short circuits, do not remove the terminals’ plastic protective caps until the battery is ensconced within the vehicle’s tray. Avoid any impacts, which might crack the casing, as well

as damaging the internal plates. Neither bare batteries, nor their pallets, should be stacked. Keep the battery clean, too. Moisture and dirt can accelerate discharge rates. Varta highlights that its representatives have an insight of the whole supply chain and can advise on the best process to suit your business, should you be unsure.


The following links are useful to identify suitable technically-compatible quality replacement batteries that match OEM specifications:



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