Search 4,528 docs, articles & videos from the world’s leading Automotive part manufacturers


Right battery, Happy Alternator

Monday 28th March 2016
Print Article

Battery choices can be overlooked and as the market is very price orientated the cheaper alternative always seems like the best way forward. Often this can be the incorrect choice and can affect the vehicle’s charging system and electrics.

There is a large selection of battery choices available in the market and the technology has changed over the years. Conventional flooded-cell, absorbent glass mat (AGM), gel-cell, silver calcium and lithium-ion batteries are types of batteries available in today’s market. Each type has its advantages and disadvantages, but the AGM type battery is the one that seems to be getting the most attention lately.

AGMs have been introduced across a wide range of vehicles over the last few years, particularly with vehicles that are equipped with start-stop systems. A typical day’s driving could require up to 50 start-stop cycles.

As vehicles technology continuously advances, the use of the correct battery type is more important than ever. BMW have a specific protocol which was introduced several year ago that requires the battery to be paired to the vehicle’s engine management system using the correct scan tool, informing the engine management system of the replacement battery type, size and age.

If the registration is not completed or actioned there can be some expensive consequences. As the engine management system recognises the type of battery used it needs to recognise the type of battery it has been replaced with. If, for example the vehicle was originally fitted with an AGM but the replacement battery is a flooded-cell battery or vice versa, the engine management system must know which type of battery is installed (AGM or flooded-cell), the engine management system could apply an incorrect charging protocol if the registration process has not been actioned. This can then result in the battery constantly being overcharged/undercharged causing damage to the battery and the vehicle’s charging/electrical systems.

Other vehicles which have smart charge systems may be fitted with silver calcium batteries and require the same type of battery fitting when replacing the battery. The incorrect battery type can cause the smart charge system to malfunction, resulting in charging faults. Information on how to test the Ford smart charge system is available via our technical support page on our website.

The Audi Q7 for example, can only have the battery replaced with an OE equivalent battery. Aftermarket batteries are not compatible with the vehicle’s engine management system. Fitting the incorrect battery results in a constant discharge. This can then result in the battery constantly being overcharged/undercharged causing damage to the battery and the vehicle’s charging/electrical systems.

A common mistake we find from alternator replacements is the incorrect use of the alternator to charge the battery. The alternator is only designed to maintain the charge of the battery and with ECU controlled alternators, they are designed to cope with the vehicle’s load demands to ensure the vehicle’s engine/electrical management systems are maintained. Fitting and using an alternator on a low charged/flat battery has a significant effect on the way the alternator functions. With smart charge technology and ECU controlled alternators, fitting an alternator to a battery in a poor state of charge will result in the alternator overcharging and will result in excessively high output readings or the alternator getting hot.

Many people will assume that the alternator will charge the battery from flat or even if it is slightly undercharged (e.g. 10v), but this is not the case. Doing this can have a major effect on the alternator and result in damage to its components.

Alternator should not be replaced until the original battery has been fully charged and load tested to ensure it is in good condition or the battery has been replaced and the correct protocol has been used when replacing it.