Ecobat warns workshops against forgetting the Auxiliary Battery.
As workshops appreciate, the days of the ‘simple’ car battery are long gone, as with the arrival of start-stop equipped, micro-hybrid vehicles and the accompanying technological change that they introduced. The battery landscape has become a lot more complicated, with the development of first AGM (absorbent glass mat) and then EFB (enhanced flooded battery) designs, to sit alongside their traditional SLI (starter, lights and ignition) counterparts.
The most recent change to this landscape is the increasing use of auxiliary batteries used to complement the main battery, usually in larger start-stop equipped applications. Although they were initially thought to be fitted to provide backup power to support the main battery or to support separate systems within the vehicle, research from Ecobat Battery, distributor of premium original equipment brands such as Exide and VARTA, has revealed that they often fulfil a more collaborative role in the vehicle’s power storage system.
Ecobat Battery’s Training Manager, Christopher Jones, takes up the story:
As a proactive business with good working relationships with our customers, we like to cooperate closely with them, which is why when we were approached by one of our dealers, that had an ongoing issue with the start-stop system in a Land Rover Discovery that was fitted with an 019 AGM battery, we were more than willing to help.
I explained that after four years, the battery could well need to be replaced because it is unable to hold sufficient charge and so had caused the start-stop function to stop working and the ECU to move the vehicles battery management system to battery save mode. Having subsequently tested the battery with our EBT780 battery tester, the battery’s state of health (SOH) was down to 70 per cent, a level that prevents the start-stop from working, in order to help reserve power, hence the light being on.
As a result, the battery was replaced, and importantly, the correct installation process followed, and was assimilated into the system using a EBT420 battery validation tool. At this point, having changed and validated the battery, the light should have gone off and the fault cleared, but instead, it came back on!
Further investigation was therefore needed, which lead us to check the auxiliary battery located on the opposite side of the engine. The reading was just 11.80 volts, so revealing an obvious problem.
Due to its SOH and also because it was of the same age as the original main battery, the auxiliary battery was then also changed and when we went back to validate the battery again, we found a question in the sub menu about both batteries being changed. After selecting this option, the warning light then went off and the start-stop function began operating normally.
This experience demonstrates that rather than simply being an ‘auxiliary’ battery, both batteries contribute to the start-stop system and due to the condition of the auxiliary battery in this example, the fault code could not be cleared and the start-stop system wouldn’t reactivate. This situation highlights two valuable lessons for workshops, first find out whether the vehicle has an auxiliary battery, and second, check that battery when they test the starting battery.
