A fully charged battery supplies around 12.6 volts. If this falls to 12.0 volts,
the power supplied drops from around 100% to around 25%.
What happens if it's not changed?
Sludge builds up in the bottom of the case and can short the cell out. Deep
discharges, heat, vibration, over-charging, under-charging or non-use all speed up
the ageing process. In the end, if not replaced the battery will fail, and one day
your car won't start.
What do we do?
We check the battery's ability to hold its charge. We may need to replace the
battery if it's not holding a charge, or look at why it's not charging when you
How often does it need to be checked?
At every service.