Munich - Batteries in seasonal cars require special care while the cars are in storage over the winter. Modern chargers ensure that the car's batteries stay fully charged and prolong their service life. Even in cars that are driven every day, batteries usually fall short of their full capacity during the winter season – recharging restores them to full power. An overview and helpful tips from TÜV SÜD's experts.
In vehicles that are stored throughout the winter, the batteries lose power automatically over time. "Self-discharge can account for as much as 30 per cent of monthly battery capacity", explains Eberhard Lang from TÜV SÜD. In newer vehicles, the on-board electronic systems also consume a significant amount of power even when idle, making recharging doubly important. To compound the problem, many drivers are unaware that in winter their battery may only have 70 to 80 per cent of its normal capacity. "In cold weather the battery cannot take up all the power the generator could produce", says Lang. In addition, large-scale power guzzlers like windscreen heating systems and in-car heaters are regularly in action in cold weather, consuming still more power.
Equipment: Many cellars and garages are still home to battery chargers that are decades old. "The technology of these chargers is completely outdated, and their compatibility with modern battery types is poor", says the TÜV SÜD specialist, adding that this applies particularly to AGM (Advanced Glass Mat) type batteries as well as other battery types, particularly those installed in cars with start-stop systems. Old battery chargers simply try to "pump" as much power as possible into the battery; when the battery is full this surplus power is turned into heat, which impairs the battery's service life. Modern chargers, however, automatically switch to maintenance charge once the battery is 100% charged. In other words, they occasionally top up the battery power to maintain a fully charged state, and also align the charging current precisely to the charging level and battery type. Extremely sophisticated models even discharge the battery slightly and then recharge if the car is immobile for long periods – a process that benefits battery life.
Voltage: 12 volts have been the standard car battery charging voltage for decades, and chargers are generally designed for this. However, classic cars and motorbikes may also have on-board electrical systems that operate on 6 volts, and 24-volt systems are widespread in commercial vehicles. Take care to check the correct voltage when buying a battery charger! Selectable-charge models are available from retailers. Ensure that the charger offers the correct charge level for the battery you plan to use it with!
Connection: In the past, the procedure was always to disconnect the battery before charging and remove the filling caps. This is no longer necessary with modern chargers. They automatically regulate the charging procedure, making boiling acid and gas formation a thing of the past. "The battery should stay connected permanently", advises Lang. It cannot harm classic cars, and will save owners of newer seasonal cars the trouble of getting to grips with electronic systems – resetting clocks and radios is a laborious procedure.
Clips: Although modern chargers are no longer sensitive to short-circuiting and reverse connections, correct connection and the right sequence of actions are still important. The first action is always to connect the charger to the battery – only then should the charger be powered up! The red clip must be connected to the positive terminal; although the marking is often poorly visible, one means of identification is that positive terminals are protected by a cap.
The waiting game: Batteries of standard cars are fully recharged after a few hours; most modern chargers have an indicator light to show this. Seasonal cars can remain connected to the charger if there is a handy electrical socket nearby; the power consumption of the charger is negligible, particularly in maintenance charge mode.
Filling: Most modern batteries are sealed; the cells no longer have removable filling caps as in the past, where the acid level could be checked. If you are still using a cap-type battery, check the level and perform any necessary topping-up before starting to use the charger. "Topping up with distilled water dilutes the acid and reduces the state of charge", explains Lang. Once the charger is connected for recharging, this reduction corrects itself. The acid level should be around one centimetre over the plates. Batteries generally have floating indicators to show the right level. Never overfill, and always use distilled water – not acid!
Care: Although battery care in winter requires some work, neglecting these tasks can be an expensive omission. "Fully discharged batteries will freeze", warns the TÜV SÜD professional. Temperatures of around -12° Celsius would completely destroy a battery. Thawing may also cause sulphuric acid to seep out of cracks in the housing, causing major damage to the engine compartment and the environment.